Prepare Your Equipment:

1. Preheat the oven to 350°F (175°C).
2. Line a muffin pan with cupcake liners for easy removal and cleanup.

2. Make the Chocolate Cupcake Batter:

1. In a medium bowl, whisk together cocoa powder, flour, baking soda, and salt.
2. In a separate large bowl, mix sugar, vegetable oil, eggs, and vanilla extract until smooth.
3. Gradually add the dry ingredients to the wet ingredients, alternating with milk. Mix until just combined.

3. Bake the Cupcakes:

1. Fill the cupcake liners two-thirds full with the batter.
2. Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.
3. Let the cupcakes cool completely on a wire rack before filling and frosting.

4. Prepare the Peanut Butter Filling:

1. In a small bowl, mix peanut butter, powdered sugar, and milk until smooth.
2. Use a cupcake corer or a small knife to remove the center of each cooled cupcake.
3. Fill each cupcake with the peanut butter mixture using a piping bag or small spoon.

5. Make the Peanut Butter Frosting:

1. In a large bowl, beat softened butter and peanut butter until creamy.
2. Gradually add powdered sugar, mixing well after each addition.
3. Add milk and vanilla extract, beating until the frosting is smooth and spreadable.

6. Frost the Cupcakes:

1. Pipe or spread the frosting onto each cupcake.
2. Garnish with chocolate shavings, chopped peanuts, or a drizzle of melted chocolate if desired.