Keto Lemon Mug Cake

This low carb and keto-friendly mug cake is bursting with lemon flavor. It’s a single serving cake that cooks in the microwave in less than two minutes.

overhead photo of a keto lemon mug cake

Lately, I have really been loving creating low carb mug cakes. When I wrote my mug cake cookbook* a few years ago, I felt like I exhausted every flavor combination possible for a regular mug cake. But low carb mug cakes are a whole different territory and it’s definitely reignited my desire to create new mug cakes.

So far I’ve made low carb snickerdoodle mug cake, blueberry mug cake, peanut butter mug cake, and brownie mug cake, just to name a few. This lemon mug cake is sweet and bright and reminds me of lemonade and summer.
photo of a lemon mug cake

Lemon Flavored Mug Cake

This cake gets its lemon flavor from both lemon juice and lemon zest. The lemon juice soaks into the batter and makes the batter ultra-moist. The lemon zest really enhances the lemon flavor throughout the cake.

I highly recommend that you take the extra minute or so it takes to grate some lemon zest for this recipe. When I first started baking many years ago, I used to always leave zest out of recipes because I didn’t think it was necessary. But especially with citrus recipes, it makes a huge difference. It really rounds out the lemon flavor so you don’t feel like you’re just eating a lemon juice cake.

Low Carb Flour Substitutes

This cake is made with a combination of superfine almond flour and coconut flour. The recipe only needs a tiny bit of coconut flour, but it is essential to this recipe coming out correctly. I prefer almond flour cakes because I find that they come out more light and moist. But a little bit of coconut flour is needed to soak up the lemon juice. Coconut flour is highly absorbent so you need to make sure you don’t add too much or it will make the cake dry.

Mug Cake Cooking Tips

  • This cake does not rise that high. I made it in an 8 oz mug.
  • Try to stick to a standard shaped mug. Mugs that are unusually tall or odd-shaped can result in the batter not cooking evenly.
  • The lemon juice tends to sink a little towards the lower half of the cake. To make sure there is enough lemon flavor throughout, I added a little bit of lemon zest to the top of the cake before cooking it.
  • The cake is best consumed shortly after it is cooked.
  • The cake can be topped with toppings of your choice. I kept it simple with some powdered Swerve.

Keto Lemon Mug Cake

Prep Time: 5 minutes
Cook Time: 2 minutes
Total Time: 7 minutes
Course: Dessert
Cuisine: American
Servings: 1

A light cake bursting with lemon flavor. This cake cooks in the microwave in less than 2 minutes!


  • 1 tbsp unsalted butter melted
  • 1 large egg
  • 3 tbsp superfine almond flour
  • ¼ tsp coconut flour
  • ½ tsp baking powder
  • 1 ½ tbsp erythritol sweetener granular
  • ¼ tsp vanilla
  • 1 tbsp lemon juice
  • ¼ tsp lemon zest plus additional for topping


  1. In a microwave-safe mug that can hold at least 8 oz of liquid, add all mug cake ingredients except lemon zest. Mix with a small whisk until batter is smooth.

  2. Stir in 1/4 tsp lemon zest. Add a little more zest over surface of the cake. This should only be about a pinch worth spread out across the surface.

  3. Cook the cake in the microwave for about 1 minute and 40 seconds. Let cake cool slightly before dusting with powdered sugar substitute (like Swerve) or other topping of your choice. Cake is best consumed shortly after it is cooked.


  • I use an 1100 watt microwave. You may need to adjust time and/or power if you are using a different wattage.
  • I used So Nourished Erythritol Sweetener Granular* but you can use any granular sugar substitute of your choice. I prefer using erythritol because it doesn't have that cooling sensation.
  • The coconut flour is essential to this recipe. The cake will not be able to asborb all the lemon juice and will not rise properly without it. At the same time, you need to make sure you only use 1/4 tsp of coconut flour. Coconut flour is highly absorbent so if you use even a little bit extra, your cake will come out dry.
  • The cake does not rise that high so using an 8 oz mug should be sufficient.
  • Adding just a little extra lemon zest to the surface of the cake will help ensure lemon flavor throughout the cake because the juice does tend to sink a little towards the bottom of the cake.
  • *Some of the links contained in this post are affiliate links. Much like referral codes, this means I earn a small commission if you purchase a product I referred (at no extra charge to you).
  • Estimated Nutrition Information does not include carbs from erythritol
Nutrition Facts
Keto Lemon Mug Cake
Amount Per Serving (1 cake)
Calories 298 Calories from Fat 234
% Daily Value*
Fat 26g40%
Saturated Fat 10g63%
Cholesterol 194mg65%
Sodium 69mg3%
Potassium 313mg9%
Carbohydrates 8g3%
Fiber 3g13%
Sugar 2g2%
Protein 10g20%
Vitamin A 592IU12%
Vitamin C 6mg7%
Calcium 177mg18%
Iron 2mg11%
Net Carbs 5g10%
* Percent Daily Values are based on a 2000 calorie diet.
The nutrition information provided are only estimates based on an online nutritional calculator. I am not a certified nutritionist. Please consult a professional nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have. All images and content are © Kirbie's Cravings.

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