In a microwave-safe mug, add flour, protein powder, baking powder, and salt. Mix thoroughly to eliminate clumps. Even distribution ensures consistent texture.

Add milk, sweetener, vanilla extract, and nut butter if using. Stir until a smooth batter forms. The consistency should resemble thick cake batter — not runny, not dry.

Adjust milk gradually if needed.

Gently stir in chocolate chips. Reserve a few for topping if desired.

Microwave on medium-high power for 40–70 seconds depending on microwave strength. Cooking time varies widely. The cake should rise and appear set but remain soft.

Avoid overcooking — this is the most common mistake.

Allow mug cake to rest for 1–2 minutes. This improves texture and prevents burns.

Eat directly from the mug or transfer to a plate.