Preheat your oven to 350°F (175°C) and grease two 9-inch round baking pans.
In a large bowl, mix flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add eggs, milk, oil, and vanilla to the dry ingredients and beat for 2 minutes.
Stir in boiling water until the batter is smooth.
Pour the batter into the prepared pans and bake for 30-35 minutes.
Let the cakes cool in the pans for 10 minutes, then transfer to wire racks.
To make the frosting, beat peanut butter and butter until creamy, then add powdered sugar and milk.
Frost the cooled cake layers and stack them.
Garnish with crushed peanuts or chocolate shavings if desired.
Slice and serve your delicious chocolate peanut butter cake.