90-Second Keto Chocolate Mug Cake
This keto chocolate mug cake is a soft, rich chocolate sponge for one, made with a sachet of Groovy Keto Chocolate Mug Cake Mix, an egg and melted butter, with dark chocolate buttons pushed into the middle so the centre turns molten. It has 2.5g net carbs. It spends about 90 seconds in the microwave and is ready to eat in 5 minutes.
This keto mug cake recipe borrows from some proven recipes. Katrin Nürnberger's keto lava mug cake on Sugar Free Londoner pushes a square of chocolate into the middle of the batter, so it melts into a gooey centre while the sponge cooks around it, and gives timings for different microwave powers. Nikki Lilly's mug cake on BBC Food melts the butter in the mug first, so the whole thing is mixed in one mug with a fork. The microwave mug cake on BBC Good Food says to use the largest mug you have so it doesn't overflow, to cook it until it has stopped rising, and to serve it with a scoop of ice cream. We've put those ideas together with our own mug cake mix and dark chocolate buttons.
The result is a warm, soft chocolate sponge with a pocket of melted chocolate in the middle, ready in minutes with almost no washing up. A slice of ordinary chocolate fudge cake of the same weight has about 62.4g carbohydrate; this keto chocolate mug cake has 2.5g net carbs. If you're searching for sugar free mug cakes, this one has no added sugar: the mix and the buttons are sweetened with erythritol and stevia, and the small amount of sugars comes from the cocoa, almonds and butter. To see where chocolate fits on a keto diet, read our guide Is chocolate keto-friendly?
What we used: a sachet of Groovy Keto Chocolate Mug Cake Mix, which already contains the cocoa, almond flour, coconut flour and sweetener and only needs butter and an egg, and Groovy Keto Dark Chocolate Buttons for the molten middle. The pack's own figure of 2g net carbs is for the mix with butter and egg; the chocolate buttons take it to 2.5g. For other flavours, see our full range of keto mug cake mixes.
Groovy Keto Chocolate Mug Cake Mix
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Groovy Keto Dark Chocolate Buttons
View productKeto mug cake vs ordinary chocolate cake
An ordinary chocolate mug cake is made with self-raising flour and a few spoonfuls of caster sugar, so most of its carbohydrate comes from starch and sugar. This one uses a mix made with almond flour, coconut flour, oat fibre and cocoa, sweetened with erythritol and stevia, and erythritol counts as a polyol, which UK labels list within carbohydrate.
| Per portion (about 112g) | Carbohydrate | Sugars | Net carbs |
|---|---|---|---|
| Chocolate fudge cake, same weight | 62.4g | 48.7g | 62.4g |
| This keto chocolate mug cake | 29.5g | 1.2g | 2.5g |
Ordinary chocolate cake figures are worked out for a 112g portion, about the weight of our mug cake once cooked, from UK CoFID 2021 data (food code 11-527, "Cake, chocolate fudge": 55.7g carbohydrate and 43.5g sugars per 100g) – McCance and Widdowson's composition of foods. Carbohydrate excludes fibre, as on UK labels. Our carbohydrate figure includes 27.0g polyols from the erythritol, which are taken off to give net carbs.
Tips for the best keto mug cake
- Use a bigger mug than you think. The cake roughly doubles in height as it cooks. A wide mug of 350ml or more stops it spilling over and helps it cook evenly.
- Beat the egg in properly. Mix for a good 30 seconds and scrape the bottom of the mug. Pockets of dry mix or egg white show up as floury or spongy patches.
- Push the chocolate into the middle. A microwave cooks from the inside, so chocolate tucked into the centre melts into a molten pocket while the sponge sets around it.
- Stop while it still looks soft. Take it out when the top looks set. It firms up during the minute's rest, and an extra 20 seconds can turn it rubbery.
- Know your microwave. The wattage is usually on a sticker inside the door. Lower-power microwaves need a few more seconds; more powerful ones need a few less.
90-Second Keto Chocolate Mug Cake
- Prep time3 min
- Microwave60 seconds
- Total time4 minutes, plus 1 minute resting
- Serves1
- Net carbs2.5g per mug cake
Ingredients
For the mug cake
- 1 sachet (50g) Groovy Keto Chocolate Mug Cake Mix
- 1 tablespoon (15g) unsalted butter
- 1 medium egg
- 10g Groovy Keto Dark Chocolate Buttons
You will also need a wide, microwave-safe mug that holds at least 350ml, a fork and a microwave.
Method
- Pick a big mug. Use a wide, microwave-safe mug that holds at least 350ml. The batter only fills it about a third of the way, but it rises well above that while it cooks.
- Melt the butter. Put the butter in the mug and microwave it for 20 to 30 seconds, until melted. Tilt the mug so the butter coats the sides, which helps the cake come out cleanly if you want to turn it out.
- Add the mix. Tip the sachet of mug cake mix into the melted butter and stir it in with a fork.
- Add the egg. Crack in the egg and beat with the fork for about 30 seconds, scraping round the bottom and sides of the mug, until the batter is smooth with no dry streaks.
- Add the chocolate. Break the chocolate buttons into a few pieces and push them into the middle of the batter until they are just covered.
- Microwave. Cook on full power for 60 seconds, as the pack says, until the cake has risen and the top looks set. If your microwave is 800W or less, it may need another 10 to 15 seconds; if it's 1000W or more, check it at 50 seconds.
- Rest. Leave the cake for 1 minute before eating, as the mug and the melted chocolate in the middle will be very hot. Eat it from the mug, or run a knife round the edge and turn it out onto a plate.
3 topping ideas
- Cream and raspberries: spoon 2 tablespoons of lightly whipped double cream on top and add a few raspberries. The cream adds about 0.5g carbohydrate and 30g of raspberries about 1.5g, using UK CoFID data.
- Keto ice cream: turn the warm cake out onto a plate and add a scoop of our homemade keto ice cream, so it melts into the sponge.
- Quick chocolate sauce: melt two or three extra chocolate buttons with 1 tablespoon of double cream in 10-second bursts in the microwave, stir until smooth and pour it over.
The nutrition figures below are for the mug cake on its own, so any topping will add to them.
Ways to change it
- Other flavours: the same method works with our other keto mug cake mixes, such as salted caramel, red velvet or gingerbread. Check each pack for its own method.
- Peanut butter centre: swap the chocolate buttons for 1 heaped teaspoon of smooth peanut butter pushed into the middle.
- Mocha: stir ½ teaspoon of instant coffee granules into the melted butter before you add the mix.
- Bigger chocolate hit: stir a few chopped chocolate buttons through the batter as well as the ones in the middle.
- Oil instead of butter: use 1 tablespoon of light olive oil or melted coconut oil, as the pack allows.
Any of these changes will alter the nutrition figures.
How to serve keto chocolate mug cake
- Straight from the mug: eat it warm with a teaspoon while the middle is still molten.
- Turned out: run a knife round the inside of the mug, turn the cake out onto a small plate and let the melted chocolate run down the sides.
- With a hot drink: it goes well with a cup of tea or coffee as an evening treat. For more ideas, see our round-up of keto sweet treats, or bake our keto chocolate cake when you're feeding a crowd.
Storage
- Best fresh: a mug cake is at its best within a few minutes of cooking, while it's warm and soft.
- Fridge: cover any leftover cake and keep it in the fridge for up to 2 days. Warm it for 10 to 15 seconds in the microwave before eating.
- Batter: don't make the batter ahead, as the raising agents start working as soon as the egg goes in.
Nutrition
Per serving (1 mug cake, without toppings):
| Nutrient | Per mug cake |
|---|---|
| Energy | 338 kcal |
| Fat | 29.6g |
| of which saturates | 13.1g |
| Carbohydrate | 29.5g |
| of which sugars | 1.2g |
| of which polyols | 27.0g |
| Net carbs | 2.5g |
| Fibre | 8.2g |
| Protein | 11.7g |
| Salt | 0.70g |
Net carbs are carbohydrate minus polyols. On UK labels, fibre is already listed separately from carbohydrate, so it isn't subtracted again. Figures are calculated from the Groovy Keto Chocolate Mug Cake Mix and Dark Chocolate Buttons pack labels and UK (McCance and Widdowson's CoFID) data for the butter (17-661) and a medium egg (12-937), and will vary with the brands you use. Excessive consumption of polyols, such as erythritol, may produce laxative effects.
Allergens: this recipe contains nuts (almonds), milk and eggs. The Chocolate Mug Cake Mix pack says it contains almonds, and that the mix is produced in a facility where there may be other nuts, milk and eggs. The Dark Chocolate Buttons pack says they are packed in a facility where there may be traces of nuts, cereals, milk and eggs. Always check the current pack labels before making it for anyone with an allergy.
FAQ
How long do you microwave a keto mug cake?
This one cooks for 60 seconds on full power, after 20 to 30 seconds to melt the butter, so it spends about 90 seconds in the microwave in total. Microwaves vary, so add 10 to 15 seconds in a low-power one, and stop as soon as the top looks set, as overcooking makes it rubbery.
Can you make a mug cake in the oven or air fryer?
This recipe is written and tested for the microwave only, following the Chocolate Mug Cake Mix pack, which gives a microwave time but no oven or air fryer times. We haven't tested it in an oven or air fryer, so we don't give times for them. For an oven bake, try our keto chocolate fudge cake instead.
How many carbs are in a keto mug cake?
This keto chocolate mug cake has 2.5g net carbs, worked out as 29.5g carbohydrate minus 27.0g polyols from the erythritol in the mix and chocolate buttons. It also has 338 kcal, 8.2g fibre and 11.7g protein. Any toppings, such as cream or berries, will add to these figures.
Why is my mug cake rubbery or dry?
It has almost always been cooked for too long. A mug cake keeps cooking for a minute after the microwave stops, so take it out when the top looks just set, even if it seems slightly soft. Beat the egg in well too, as streaks of egg white turn spongy.
Can I use oil instead of butter?
Yes. The pack says you can use 1 tablespoon of oil instead of the butter, so a light olive oil or melted coconut oil both work. Melted butter gives the richest flavour. The nutrition figures here are worked out with butter, so they will change slightly if you use oil.
Can you make a keto mug cake ahead?
It's best eaten warm, within a few minutes of cooking. If you have some left, cover the mug and keep it in the fridge for up to 2 days, then warm it for 10 to 15 seconds in the microwave. Don't mix the batter in advance, as the raising agents start working once the egg goes in.
