Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round baking pans.
In a large mixing bowl, combine the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add the eggs, milk, oil, and vanilla extract to the dry ingredients and mix until well combined.
Stir in the boiling water until the batter is smooth. The batter will be thin.
Pour the batter evenly into the prepared pans. Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes, then remove them from the pans and cool completely on a wire rack.
For the frosting, beat the peanut butter and butter together until smooth. Gradually add the powdered sugar, mixing until well combined. Add the milk and beat until the frosting is light and fluffy.
Frost the cooled cakes with the peanut butter frosting. Serve and enjoy!