Melt the butter in a small bowl in the microwave, letting it cool slightly.
Combine the flour, sugar, baking powder, and salt in an 8 oz. microwave-safe mug; stir in the chocolate chips.
Add the milk and vanilla to the melted butter; gently pour the liquids into the flour mixture, stirring just until the ingredients are combined to make the batter. Don’t over-mix.
Scrape down the sides of the mug so it is clean inside. Microwave the mug cake on high power for 50-60 seconds. **This cooking time can vary depending on how your microwave cooks. In my microwave, 50 seconds makes the perfect mug cake doneness.
Test the mug cake for doneness by inserting a toothpick into the center of the cake. If it comes out clean, the mug cake is done. If the toothpick has batter clinging to it at when you test the center, give the mug cake 10 more seconds of cooking time.
Serve the mug cake immediately while still warm, topped with whipped cream and a sprinkle of more chocolate chips, as desired. Mug cakes are also delicious topped with chocolate frosting!
Notes
An 8-ounce mug works great for making this mug cake. The mug should be about one-third full of batter when you get ready to cook it. Once the mug cake is fully cooked, the mug will be almost two-thirds full of cake.
Don’t over-mix the batter for the mug cake. Over mixing can activate the gluten causing the texture of the mug cake to be kind of chewy and tough.
Don’t overcook the mug cakes. When you remove them from the microwave, they may still look a bit doughy on top so don’t be fooled.
To test the mug cake for doneness, do use a toothpick inserted into the center to see if it’s fully baked. If you insert the toothpick into the center and it comes out clean, the cake is done. If there’s batter clinging to the toothpick, give it 10 more seconds of cooking time.
Mug cakes are meant to be served warm, right after you’ve made them, not later. Think of mug cakes as a treat to enjoy on the spot, right when your sweet tooth is hollering.