1. Preheat oven to 350°F. Coat 2, 9-inch cake pans with nonstick spray. Cut 2, 9-inch rounds of parchment paper and place in the bottoms of the pans. Spray again with nonstick spray. Set aside.
2. In the bowl of your stand mixer fitted with the paddle attachment, mix together the sugar, flour, cocoa powder, baking soda, baking powder, and salt on low speed until combined.
3. With the mixer still on low, add in the eggs, milk, vegetable oil, and vanilla. Turn mixer up to medium and mix for 2 minutes, scraping the sides of the bowl as necessary. Turn the mixer back down to low and slowly add in the hot water. Mix for an additional minutes until combined.
4. Divide the batter between the 2 prepared pans. Bake for 30 minutes, or until a toothpick inserted in the center comes out clean.
5. Allow the cake to cool in the pan for 10 minutes and then remove and transfer to a wire rack to cool completely.

Peanut Butter Filling

1. In the clean bowl of your stand mixer, fitted with the paddle attachment mix the butter and peanut butter together on medium speed until smooth. Turn the mixer to low and slowly add in the powdered sugar. Turn the mixer to medium and mix for 1 minute until combined.
2. Turn mixer back to low and add in 1/4 cup milk. Mix for an additional minute, scraping the sides of the bowl as necessary, until creamy and combined. If desired, add additional milk to achieve desired result.
3. Transfer one of the cooled cakes to a plate or cake stand. Spread the peanut butter filling on top of the cake. Place the other cake on top of the peanut butter filling.

Chocolate Frosting

1. In the bowl of your stand mixer fitted with the paddle attachment, combine the butter, cocoa powder, powdered sugar, vanilla, and warm water and mix on low speed, until the mixture just comes together.
2. Slowly increase the speed to medium and beat the frosting for 2 minutes, scraping the sides of the bowl as necessary.
3. Let the frosting cool for 15 minutes before covering the cake.

Garnish

1. Once you have the cake covered in the chocolate frosting, pile the chopped peanut butter cups on top. Next, sprinkle 2 cup of the milk chocolate chips on top and around the bottom of the cake.
2. Place the remaining 1/4 cup chocolate chips and 1 1/2 milk into a microwave-safe bowl. Heat in 15 second increments, stirring in between each, until the chocolate is smooth. Place the melted chocolate into a small zip-top bag and snip the corner off. Drizzle the melted chocolate all over the cake.