For the Chocolate Cake:

1. Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
2. In a large bowl, combine the flour, sugar, cocoa powder, baking powder, and salt. Mix well.
3. Add the milk, vegetable oil, eggs, and vanilla extract to the dry ingredients. Beat on medium speed until smooth.
4. Carefully stir in the boiling water. The batter will be thin, but that’s normal.
5. Divide the batter evenly between the prepared cake pans.
6. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
7. Let the cakes cool in the pans for 10 minutes before transferring to a wire rack to cool completely.

For the Peanut Butter Frosting:

1. In a large bowl, beat together the peanut butter and unsalted butter until smooth and creamy.
2. Gradually add the powdered sugar, 1/2 cup at a time, mixing until smooth after each addition.
3. Add the milk and vanilla extract, and beat until the frosting is light and fluffy.
4. If the frosting is too thick, add a little more milk until it reaches your desired consistency.

Assembling the Cake:

1. Once the cakes have cooled completely, place one layer of the chocolate cake on a serving plate.
2. Spread a generous amount of peanut butter frosting on top of the first layer.
3. Place the second cake layer on top and frost the top and sides of the entire cake with the remaining peanut butter frosting.
4. Optionally, you can garnish the top with chopped peanuts or chocolate shavings for added texture and decoration.