Preheat oven to 350°F. Spray (3) 9" round baking pans with non stick spray. Set aside. Unwrap and cut 12 Reese's cups into quarters. Place the remaining peanut butter cups into the fridge to chill.
Cut butter into chunks and place it in a large microwave safe mixing bowl, melt completely. Add sugar, cocoa, vanilla and eggs. Mix with an electric mixer on medium, until combined. Add remaining ingredients. Mix until completely combined, but do not over mix.
Divide evenly into prepared baking pans. Sprinkle quartered Reese’s Peanut Butter Cups over batter, press into batter with a spatula until they are even with the brownie mixture. Bake for 20 minutes or until a tooth pick comes out clean. Place in the freezer to cool, about 15 minutes.
Combine cream cheese, butter and peanut butter in a large bowl and mix with an electric mixer (or stand mixer fitted with a paddle attachment). Beat on medium speed until smooth and creamy, about 3 minutes. Add sugar. Beat on low until combined, then switch to medium speed and beat until light and creamy. Add vanilla and salt. Beat mixture until well combined.
Place a dollop of frosting on a 10" plate. Place first brownie layer on plate. Spread about 1/2 cup frosting over top of cooled brownie. Place second layer and spread about 1/2 cup frosting over top. Frost the top and sides like a cake.
Unwrap Reese's and cut them all in half. Place halved peanut butter cups around the bottom of the cake with the cut side down. Cut remaining Reese's halves into bite size pieces and sprinkle over the top of the cake.
Serve and enjoy.
Notes
This cake freeze very well. Be sure to wrap well and defrost for 30 minutes before eating.