In a small bowl, whisk together four, cocoa powder, sugar, and baking powder until thoroughly,completely combined with no streaks of flour or cocoa powder remaining.
In another bowl blend milk, butter, and vanilla until it's smooth.
Combine both bowls of ingredients together and whisk.
Pour batter into a 14 ounce (or larger) microwave-safe mug with straight sides.
In a bowl combine peanut butter and chocolate chips.
Gently press down the peanut butter and chocolate chips in the center of the mug till even with the batter.
Microwave on high for 1 minute.
Allow to cool for a couple minutes before serving.