Choose the right mug. Pick a microwave-safe mug that holds at least 10–12 ounces. This gives the cake room to rise without spilling over.

Melt the butter. Add 1 tablespoon butter to the mug and microwave for 20–30 seconds until melted. Swirl to coat the sides, or brush the inside for easy release.

Combine dry ingredients. Add 3 tablespoons almond flour, 1 tablespoon cocoa powder, 1–2 tablespoons keto sweetener (to taste), 1/4 teaspoon baking powder, and a small pinch of salt to the mug. Stir well to break up any clumps.

Add wet ingredients. Crack in 1 large egg and add 1/2 teaspoon vanilla extract. Stir with a fork until the batter is smooth and no streaks of egg remain. If using, fold in 1 tablespoon sugar-free chocolate chips or 1 teaspoon peanut butter.

Microwave in short bursts. Cook on high for 45–60 seconds, then check. If the center is still glossy, continue in 10–15 second bursts until just set. Total time is usually 60–90 seconds depending on your microwave.

Rest, then top. Let the cake sit for 30–60 seconds to finish setting. Add a dollop of whipped cream, a drizzle of sugar-free chocolate, or a few berries if you like.

Enjoy warm. The texture is best when it’s freshly cooked and slightly warm, like a mini lava cake if you pull it early or a soft sponge if fully set.