Make the Chocolate Cupcakes:

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners.
2. Mix the Dry Ingredients: In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
3. Combine Wet Ingredients: In a separate bowl, whisk the eggs, buttermilk, vegetable oil, and vanilla extract until well combined.
4. Combine Wet and Dry Ingredients: Gradually add the wet ingredients to the dry ingredients and mix until smooth.
5. Add Hot Water: Stir in the hot water to thin the batter. It will be runny, which is normal for a moist cupcake.
6. Fill the Muffin Tin: Divide the batter evenly among the cupcake liners, filling each about two-thirds full.
7. Bake the Cupcakes: Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Allow the cupcakes to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.

Prepare the Peanut Butter Filling:

8. Mix the Filling: In a medium bowl, combine the peanut butter, powdered sugar, vanilla extract, butter, and a pinch of salt. Stir until smooth and well combined. The mixture should be thick but spreadable.

Prepare the Chocolate Ganache:

9. Heat the Cream: In a small saucepan, heat the heavy cream over medium heat until it begins to simmer.
10. Make the Ganache: Pour the hot cream over the chopped semisweet chocolate in a heatproof bowl. Let it sit for a minute, then stir until smooth and glossy. Add butter and vanilla extract, stirring until fully combined. Allow the ganache to cool slightly before using.

Assemble the Cupcakes:

11. Create a Hole for the Filling: Once the cupcakes are completely cooled, use a small knife or cupcake corer to remove a small portion from the center of each cupcake, creating a hole for the peanut butter filling.
12. Fill with Peanut Butter: Spoon or pipe the peanut butter filling into the hollowed-out center of each cupcake. Be generous with the filling!
13. Top with Ganache: Spoon or drizzle the chocolate ganache over the top of each filled cupcake, allowing it to gently overflow over the edges.
14. Let the Ganache Set: Allow the ganache to set at room temperature for about 10-15 minutes before serving.