In a microwave-safe mug (12 to 14-ounce), mix together all your dry ingredients: flour, cocoa powder, sugar, baking powder, and salt until well combined.
Next, incorporate your wet ingredients into the mix: add sour cream, the egg yolk, and a splash of vanilla extract. Stir gently until the mixture is just combined and smooth.
Carefully add the chocolate chips to the batter, folding them in slowly to ensure an even distribution without overmixing.
Place your mug in the microwave and cook on high for 1 to 1½ minutes. The cake should rise and appear slightly set with a gooey molten center.
Allow the mug cake to cool for about a minute before diving in!
Notes
This recipe is perfect for a quick dessert.
Adjust cooking time based on microwave wattage.
Try different types of chocolate chips for variety.