• Preheat the oven to 350° F.
• Prepare your 9-inch round baking pans with melted butter (1 tablespoon) by using a pastry brush to coat the butter on the bottom and sides of each baking pan. Add a little cake mix (1-2 tablespoons or more if needed) to each pan. Shake your pan to evenly distribute the cake mix to the bottoms and sides.
• In a medium bowl add the cake mix, milk (1 cup), butter (1/2 cup), eggs (4), sour cream (3 tablespoons), and brewed coffee (1 tablespoon). Mix with a mixer on medium speed for 2-3 minutes or until fully incorporated. Use a spatula to scrape the sides of the bowl halfway through mixing.
• Add in the vanilla extract (1 teaspoon) and mix until fully incorporated.
• Pour into cake pans and bake for 24-27 minutes or until a toothpick comes out clean.
• Remove from the oven and cool for 5 minutes before removing the cake from the pans.
• Remove the cakes from the pans and place them on cooling racks for 20 minutes or until completely cool.
• Once cooled place one of the cakes upside down onto a serving platter.

To Make the Frosting

• In a medium bowl add the butter (1 cup), smooth peanut butter (1 cup), honey (3 tablespoons), milk (2 tablespoons), vanilla extract (1 teaspoon), and salt (1/4 teaspoon).
• With a hand mixer mix for 3-5 minutes or until light and fluffy. Use a spatula to scrape the sides of the bowl halfway through mixing. 
• Add the sifted powdered sugar (1/2 cup + 1 tablespoon) to the bowl and mix for 2-3 additional minutes until light and fluffy. Use a spatula to scrape the sides of the bowl halfway through mixing. 
• Spoon half of the frosting on the top of the cooled cake layer you placed on the cake plate. Spread evenly over the cake while not allowing the frosting to spill over the sides.
• Gently place the other cake layer right side up on top of the frosting.
• Spoon the remainder of the frosting on top of the cake. Spread evenly over the cake while not allowing the frosting to spill over.
• Cut 10 mini Reese's Peanut Butter Cups in half. Gently pile them on top of the frosting along with 10 whole Reese’s Peanut Butter Cups.