- 3 tablespoons chocolate chips, or to taste
- 2 tablespoons butter
- 2 tablespoons packed brown sugar
- 1 tablespoon white sugar
- salt
- 1 pinch baking soda
- 1 splash vanilla extract
- 1 egg yolk
- 1/4 cup all-purpose flour
- Microwave chocolate chips and butter in a microwave-safe mug until melted, about 20 seconds. Add brown sugar, white sugar, salt, baking soda, and vanilla extract; mix together until combined. Stir in egg yolk. Add flour; mix until batter is blended and smooth.
- Cook in the microwave until crust forms but center is still fudgy, about 35 seconds. Add 5 to 10 seconds for a drier consistency.