Gather ingredients in a microwave-safe mug (ceramic or glass, 10–12 ounces capacity): Combine 2 tablespoons almond flour, 1 tablespoon coconut flour, 1 tablespoon cocoa powder, 0.25 teaspoon baking powder, and pinch of salt. Use a fork to break up any clumps. Checkpoint: You should see no lumps in the dry mixture and it should look like fine breadcrumbs.

Add wet ingredients: Add 1 tablespoon softened butter, 1 large egg, 2 tablespoons heavy cream, 1 teaspoon vanilla extract, and 1 tablespoon erythritol or monk fruit sweetener to the same mug. If using instant coffee powder for deeper flavor, add a pinch now.

Mix thoroughly for 30–45 seconds using a fork, scraping the bottom and sides of the mug repeatedly to combine all ingredients. Stir until batter is smooth, consistent, and no streaks of egg white remain. Checkpoint: The batter should look like thick chocolate pudding with no visible dry flour.

Optional: Add chocolate chips by folding 1 tablespoon sugar-free chocolate chips into the batter for melty pockets of richness.

Microwave on high power for 60–90 seconds. Start checking at 60 seconds. The cake is done when the top is set and springy to the touch but still very slightly moist in the center—it will continue cooking from residual heat. Do not overmicrowave or the cake will be dry and rubbery. Checkpoint: A toothpick inserted in the center should show some moist crumbs, not raw batter. If the mug feels extremely hot, use an oven mitt.

Cool for 1–2 minutes in the mug before eating. This allows the cake to set and become easier to eat without burning your mouth.

Optional: Top with garnishes such as 1 tablespoon whipped cream, a few fresh raspberries, a drizzle of sugar-free chocolate sauce, or a small dollop of almond butter for extra richness.