1. Preheat oven to 350°F. Line 12 muffin tins with paper liners.
2. Place the peanut butter, egg, sugar and vanilla in a mixing bowl and beat with an electric mixer on medium speed until smooth.
3. With the mixer on low speed, slowly add half of the milk.
4. Sift the flour and baking powder together.
5. Gradually fold in half of the flour mixture, the remaining milk and the rest of the flour mixture.
6. Fill each baking cup 3/4 full. Bake until a skewer inserted into the middle of a cupcake comes out clean, about 20 to 25 minutes. Allow the cupcakes to cool for 5 minutes before removing them from the pan.
7. When the cupcakes are cool, melt the chocolate over a double boiler. Let the chocolate cool until it thickens slightly. Using a spoon, drizzle the cupcakes with the melted chocolate.
Makes 12 standard sized cupcakes or 24 miniature cupcakes.Serving Size: 1 cupcake