Choose the right mug: Use a microwave-safe mug that holds at least 10–12 ounces. A wider mug cooks more evenly.
Combine dry ingredients: In the mug, whisk almond flour, cocoa powder, sweetener, baking powder, and salt until no lumps remain.
Add wet ingredients: Add the egg, melted butter, almond milk, and vanilla.
Whisk with a fork until the batter is smooth and uniform.
Fold in extras: If using chocolate chips or nuts, gently stir them in. Keep mix-ins minimal to avoid overfilling the mug.
Microwave: Cook on high for 45–60 seconds to start. The top should look just set but still slightly glossy in the center.
Check doneness: If it’s too wet, continue in 10-second bursts. Do not overcook—it will firm up as it rests.
Rest and serve: Let stand 1–2 minutes.
Add your favorite keto-friendly topping and enjoy warm.