Use a microwave-safe mug (10–12 oz). Lightly grease if needed.
Whisk the egg in the mug.
Add cocoa powder and sugar-free syrup; whisk until smooth and glossy with no cocoa lumps.
Microwave on high 30–60 seconds, until the top looks set but the center is still slightly soft (don’t overcook).
Rest 1 minute before eating (it keeps setting as it sits).
