Step 1: Prepare the Chocolate Cupcake Batter

1. Preheat oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners.
2. In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
3. In a large mixing bowl, beat butter, granulated sugar, and brown sugar until light and fluffy.
4. Add eggs one at a time, beating after each addition. Stir in vanilla extract.
5. Alternate adding dry ingredients and buttermilk, mixing on low speed. Start and end with dry ingredients.
6. Slowly mix in hot water or coffee until batter is smooth.

Step 2: Fill & Add Peanut Butter Filling

1. Fill each cupcake liner halfway with chocolate batter.
2. In a small bowl, mix peanut butter and powdered sugar until smooth.
3. Spoon 1 teaspoon of peanut butter filling into the center of each cupcake.
4. Cover with more cupcake batter, filling each liner about 3/4 full.

Step 3: Bake the Cupcakes

1. Bake for 18-22 minutes or until a toothpick inserted near the edge comes out clean.
2. Let cupcakes cool in the pan for 5 minutes, then transfer to a cooling rack.

Step 4: Prepare the Peanut Butter Cookie Topping

1. In a bowl, cream together butter, peanut butter, brown sugar, and granulated sugar until smooth.
2. Beat in egg and vanilla extract.
3. Stir in flour, baking soda, and salt until just combined.
4. Roll dough into 1-inch balls, slightly flatten, and bake at 350°F (175°C) for 8-10 minutes. Let cool.

Step 5: Assemble the Cupcakes

1. Place a cooled peanut butter cookie on each cupcake.
2. Drizzle with melted chocolate.
3. Sprinkle with chocolate chips and peanut butter candy pieces.