Preheat the Oven: Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.

Make the Cupcake Batter: In a bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt. In another bowl, beat the granulated sugar, brown sugar, eggs, buttermilk, vegetable oil, and vanilla extract until combined. Gradually add the dry ingredients into the wet ingredients and mix until smooth. Add the hot water and stir until the batter is well combined.

Prepare the Peanut Butter Filling: In a separate bowl, mix the creamy peanut butter and powdered sugar together until smooth. Roll the peanut butter mixture into small balls (about 1 tsp each).

Assemble the Cupcakes: Fill each cupcake liner halfway with batter, then place a peanut butter ball in the center. Cover with more cupcake batter until the liner is about ¾ full.

Bake the Cupcakes: Bake for 18-20 minutes, or until a toothpick inserted into the edges of the cupcakes comes out clean. Be sure to check that the center remains soft and gooey.

Cool & Serve: Allow the cupcakes to cool for a few minutes before serving. Optionally, top with whipped cream or drizzle with melted chocolate.