Preheat the oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners.

In a large bowl, whisk together the all-purpose flour, granulated sugar, unsweetened cocoa powder, baking soda, baking powder, and salt.

Add the egg, buttermilk, vegetable oil, and 1 teaspoon vanilla extract to the dry ingredients. Mix until combined.

Stir in the hot water until the batter is smooth and thin.

Divide the batter evenly among the cupcake liners, filling each about halfway.

Bake for 18 to 20 minutes, or until a toothpick inserted into the center comes out clean.

Let the cupcakes cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.

To make the frosting, beat the softened butter and creamy peanut butter together until smooth and creamy.

Gradually add the powdered sugar, mixing on low speed until incorporated.

Add 2 to 3 tablespoons heavy cream and the remaining 1 teaspoon vanilla extract, then beat for 2 to 3 minutes until the frosting is light and fluffy.

To make the ganache, place the semi-sweet chocolate chips in a heatproof bowl.

Heat ¼ cup heavy cream in a small saucepan until it just begins to simmer, then pour it over the chocolate chips.

Let the mixture sit for 2 minutes, then stir until smooth and glossy. Cool slightly before using.

Frost the completely cooled cupcakes with the peanut butter frosting using a piping bag or knife.

Drizzle the chocolate ganache over the frosting, then serve and enjoy.