Choose the right mug. Use a microwave-safe mug that holds at least 12 ounces.
This prevents overflow and gives the batter room to rise.
Melt the butter. Add the butter to your mug and microwave in short bursts until melted. Swirl to coat the sides to help prevent sticking.
Whisk the wet ingredients. Add the egg, heavy cream, and vanilla to the melted butter. Whisk with a fork until smooth and fully combined.
Add the dry ingredients. Stir in almond flour, cocoa powder, sweetener, baking powder, and a pinch of salt.
Mix until no dry pockets remain. The batter should be thick but pourable.
Fold in extras. If using sugar-free chocolate chips or nuts, gently fold them in. Don’t overmix.
Microwave carefully. Cook on high for 45–70 seconds, depending on your microwave’s power.
Start at 50 seconds and add 5–10 second bursts until the center is just set.
Check for doneness. The top should look slightly glossy but spring back lightly when touched. A slightly gooey center makes it taste like a lava cake.
Rest briefly. Let it sit for 1–2 minutes. This helps the cake finish setting and keeps it tender.
Top and serve. Add whipped cream, berries, or a sprinkle of cocoa.
Enjoy warm, straight from the mug.