Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add the eggs, milk, oil, and vanilla extract to the dry ingredients. Beat on medium speed until well combined.
Stir in the boiling water until the batter is well combined. The batter will be thin.
Pour the batter evenly into the prepared cake 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 from the pans and cool completely on a wire rack.
For the frosting, beat the peanut butter and softened butter together until creamy. Gradually add the powdered sugar, beating until smooth. Add the vanilla extract and enough milk to reach the desired consistency.
Frost the cooled cakes with the peanut butter frosting. Enjoy!