Optional toppings for serving: vanilla frozen yogurtnonfat vanilla Greek yogurt, whipped cream, extra chocolate chips, a dollop of extra nut butter
In the bottom of a 12-ounce microwave-safe mug, stir together the flour, cocoa powder, baking powder, and salt.
Add the milk, Greek yogurt, maple syrup, and peanut butter. With a fork, stir until smoothly combined. Stir in the chocolate chips.
Place the mug on a paper towel in the microwave to catch any drips. Microwave on HIGH for 90 seconds, just until a toothpick inserted near the edge comes out with a few moist crumbs clinging to it. The center will be batter-like and molten. Do not over microwave or the cake will be dry. It may take a little experimenting, depending upon the power of your microwave and width of your mug. Wider mugs will cook more quickly, while taller, narrower mugs may need a little more time.
Let cool at least 3 full minutes (the cake will continue to cook a bit as it cools, and the cake will be very hot). Add any desired toppings. DEVOUR.
The exact cook time of the chocolate mug cake may vary based on the power of your microwave. Mine is 1000 watts. It will also vary based on your coffee mug. Taller, narrower mugs may need a bit more time, while wider mugs may need less. (I developed the recipe in this 12-ounce coffee mug).
TO STORE: Microwave mug cakes are meant to be enjoyed the day they are made, so I cannot offer tips for leftovers. You could try reheating any leftovers in the microwave, but I think the cake would dry out, so at that point, I'd recommend embracing the easiness of this recipe and making a fresh one.