Melt butter in a small bowl in the microwave and let cool slightly.
Mix flour, sugar, baking powder, and salt in a microwave-safe mug.
Stir in milk, vanilla, and the melted butter.
Stir in chocolate chips.
Scrape down the sides of the mug so they are clean.
Microwave for 60-75 seconds on high.
Let cool for a minute or two.
Top with whipped cream and more chocolate chips, if desired.
Notes
Expert Tips: - Use a straight-sided mug so that it’s easy for the cake to rise.- Mix your batter to make sure there isn’t a big chunk of flour at the bottom, but don’t overmix.- Scrape down the batter in the mug and wipe down the sides and rim before baking so that your mug cake cooks evenly.- It’s tempting to melt the butter in the same mug you will use to bake the cake, but this will warm up your mug and melt your chocolate chips as you stir them into the batter.- Make sure to let the cake cool a little before eating, because it is quite hot when it comes out!- Test this recipe with your microwave: all microwaves are different, and you may find you need more or less time to bake your mug cake. And of course, if you like a gooey cake, you can reduce the cooking time a little.