Keto Rhubarb Mug Cake

Name: Keto Rhubarb Mug Cake
Prep time: 10 min
Cook time: 2 min
Total time: 12 min
Ingredients: 5 tablespoons almond flour; 2 tablespoons allulose (or other low carb sweetener); 1 large egg; 1/4 teaspoon vanilla extract; 1/4 teaspoon cinnamon; 1/4 teaspoon baking powder; 1 tablespoon oil (or melted butter); 2 tablespoons stewed rhubarb (cook ahed)

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Enjoy rhubarb season with this keto rhubarb mug cake for a great balance of sweet and tart flavors. Made with almond flour, warm cinnamon, and tangy stewed rhubarb, this single-serving cake is fluffy, moist, gluten-free and ready in just a few minutes.

Whether you’re craving an afternoon treat or an easy low-carb dessert after dinner, this mug cake delivers all the comforting flavors of a traditional rhubarb cake with a fraction of the carbs.

A hand holds a spoonful of mug cake topped with whipped cream, with the mug and utensils on a white plate and striped napkin in the background.

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Is Rhubarb Low Carb?

Yes! Rhubarb is naturally low in carbohydrates, making it a great ingredient for keto and low-carb baking. With only about 2.7g net carbs per 100g, it adds plenty of tart, fruity flavor without significantly increasing the carb count.

Because rhubarb is naturally sour, it’s often sweetened before use. For keto recipes, simply use a low-carb sweetener such as monk fruit, erythritol, or allulose.

Tip: Only eat the stalks of rhubarb. The leaves contain compounds that are toxic and should never be consumed.

Why You’ll Love This Keto Rhubarb Mug Cake

Ready in under 5 minutes
Low carb and keto-friendly
Single-serving dessert
Made with simple pantry ingredients
Delicious balance of sweet and tart flavors
Gluten-free and grain-free

A white cup filled with a hot drink topped with whipped cream, placed on a saucer and striped towel, next to two spoons and vibrant red keto rhubarb mug cake in the background. — We smothered our keto rhubarb mug cake with cream!

Ingredients

Gather your ingredients and get ready for dessert!

Almond Flour – Almond flour creates a soft, tender crumb while keeping the cake low in carbohydrates. Use finely ground almond flour for the best texture.

Sweetener – A granulated keto sweetener such as erythritol, monk fruit sweetener, or allulose works well in this recipe.

Rhubarb – Stewed rhubarb adds moisture and a pleasant tartness. Be sure to sweeten the rhubarb with a keto-friendly sweetener when stewing it.

Cinnamon – A touch of cinnamon complements the rhubarb and adds warmth to every bite.

Butter or Oil – Either melted butter or coconut oil helps keep the cake moist and rich.

How To Make Keto Rhubarb Mug Cake

The rhubarb will need to be cooked before use in this mug cake. To make stewed rhubarb, simply chop the rhubarb into small pieces and cook it in a saucepan with a little water and your favorite keto sweetener for 5–10 minutes, or until softened. Allow it to cool before measuring and adding it to the recipe.

A white mug of tea with milk being poured, next to a glass jar of stewed rhubarb, several pieces of raw rhubarb, and a keto rhubarb mug cake on a light countertop.

Beat the egg and add the oil and vanilla.

A mug filled with baking ingredients, a few pieces of raw rhubarb, and a small jar of cooked rhubarb are arranged on a light surface—perfect for making a quick keto rhubarb mug cake.

Mix in almond flour, sweetener, baking powder and cinnamon.

A small white bowl of custard-like keto rhubarb mug cake with rhubarb on top, being stirred with a spoon; pieces of fresh rhubarb lie beside the bowl on a light surface.

Stir in the cooked rhubarb.

A white mug filled with a freshly baked keto rhubarb mug cake sits on a light gray textured surface.

Microwave until firm.

Recipe Tips

Don’t overmix – Stir just until the batter comes together to keep the mug cake light and fluffy.
Use room-temperature ingredients for a smoother batter.
Check cooking time carefully – Microwave strengths vary, so start at 90 seconds and add short bursts if needed.
Use fine almond flour – This gives a softer, less grainy texture.
Adjust sweetness to taste – Rhubarb can be quite tart, so add a little extra keto sweetener if needed.
Let it rest briefly – Allow the mug cake to sit for 1–2 minutes after cooking to finish setting.
Add texture if you like – A few chopped nuts or a sprinkle of cinnamon on top works well.

Variations

If you enjoy this cake, try other variations of it with these suggestions.

Rhubarb and Strawberry – Add a tablespoon of diced strawberries for a classic flavor combination.
Rhubarb Crumble Mug Cake – Sprinkle chopped almonds and a pinch of cinnamon on top before cooking.
Lemon Rhubarb Mug Cake – Add a little lemon zest to brighten the flavors even further.

Storage

This mug cake is best enjoyed fresh. However, you can prepare the batter ahead of time and store it in the refrigerator for up to 24 hours before cooking.

serving Suggestions

Enjoy warm straight from the mug for a quick, comforting low-carb dessert.
Top with a spoonful of keto whipped cream for extra indulgence.
Add a dollop of full-fat Greek yogurt or coconut yogurt for a tangy contrast.
Sprinkle with cinnamon or a little extra sweetener before serving.
For a more dessert-style treat, serve with a few fresh berries on the side.
Drizzle with a small amount of melted butter or sugar-free syrup for added richness.

Can This Be Made In The Oven?

Yes — this keto rhubarb mug cake can also be made in the oven.

Simply transfer the batter into a lightly greased ramekin or small oven-safe dish and bake at 180°C (350°F) for about 15–18 minutes, or until the centre is set and a skewer comes out mostly clean.

Oven Tips

Use a small ramekin so the cake rises properly.
Don’t overbake, as almond flour cakes can dry out quickly.
Let it cool for 2–3 minutes before serving so it firms up slightly.

The texture will be a little more “cake-like” compared to the microwave version, but just as delicious.

A keto rhubarb mug cake topped with whipped cream sits on a saucer, with a spoonful of cake placed beside it on a white surface.

FAQs

Can I use coconut flour instead of almond flour?

Not directly. Coconut flour absorbs much more liquid and would require adjusting the recipe significantly.

Can I freeze this mug cake?

Because it is a single-serving dessert, it is best made fresh rather than frozen.

What sweetener works best?

Monk fruit sweetener, erythritol blends, and allulose all work well in this recipe.

A keto rhubarb mug cake topped with whipped cream sits on a white plate, with a spoonful of cake resting on the counter beside it.

More Easy Keto Mug Cakes

If you enjoyed this keto rhubarb mug cake, be sure to try: