Preheat oven to 325°. Spray a 6-hole donut pan with nonstick cooking spray.
Mix peanut butter and sugar with a mixer until fluffy. Add milk, oil, eggs, and vanilla; mix. Stir baking powder, salt, and flour into wet mixture. Mix just until combined. Place your dough into a large Ziploc bag and cut off the tip. Pipe evenly into the donut pan.
Bake for 8-10 minutes. Cool a few minutes in pan before removing to a wire rack to cool completely.
When donuts are cool, melt your chocolate according to package directions. Place a wire rack over a cookie sheet. Place the donuts in the chocolate, covering the entire bottom half. Place chocolate-side up on the wire rack and chill to harden. Repeat the dipping process, covering the other half of the donut with chocolate. Sprinkle with chopped peanut butter cups while still wet. Let harden and enjoy!