Step 1

Add the flour and granulated sugar to a 14-ounce microwave-safe mug. Stir to combine.

Step 2

Add the peanut butter, milk, melted butter, and vanilla. Stir to incorporate completely.

Step 3

Cook in the microwave for 1 minute 30 seconds to 1 minute 45 seconds (the time needed to cook the cake will vary depending on your microwave).

Step 4

Allow the cake to cool for a few minutes before serving. While the cake is cooling, you can dollop 1 tablespoon of peanut butter on top of the cake. The heat from the cake will melt the peanut butter. You can gently spread the peanut butter over the top of the cake to completely cover the surface.