Preheat the oven to 350 degrees. Spray 3 8-inch round cake pans with cooking spray and line the bottoms with parchment paper. Spray the paper with cooking spray and set pans aside.

Combine all ingredients in a large mixing bowl and beat for 2 minutes with an electric mixer. Divide evenly between the prepared pans. Bake 22 to 28 minutes, until a cake tester inserted into the center of the cake comes out clean. Cool in pans for 20 minutes, then carefully invert onto a wire rack to cool completely before filling and frosting.

While cake layers are in the oven, make your caramel sauce.

Combine the sugar, butter, water, and salt in a medium saucepan set over medium heat. Bring to a boil, stirring constantly, and boil for 4 minutes. Remove from the heat and stir in the evaporated milk and vanilla. Set aside to cool.

Place the butter in a medium saucepan and melt over medium heat. Stir in the sugar and evaporated milk, then bring to a simmer. Simmer 4 to 5 minutes, stirring constantly, then remove from the heat. Add the marshmallow creme, peanut butter, cocoa powder, and vanilla extract and stir vigorously until completely combined. Let cool at room temperature, stirring occasionally.

Set one cake layer on a cake stand or cardboard cake circle and spread half of the filling in an even layer over the cake. (An offset spatula dipped in hot water is helpful here.) Spread 2 tablespoons of caramel sauce over the filling. Top with another cake layer, pressing down lightly. Repeat with remaining filling and cake layer—you’ll have leftover caramel sauce. Refrigerate until filling is set, about 1 hour.

Place the butter in the bowl of a stand mixer fitted with the paddle attachment and beat until very smooth. Add 3 cups of the powdered sugar, the cocoa powder, 3 tablespoons of the milk or cream, and the vanilla, espresso powder, and salt. Mix on low until well combined, stopping a few times to scrape the sides and bottom of the bowl. Turn mixer to high for 3 to 4 minutes, beating until frosting is very light and fluffy. Add additional powdered sugar if frosting is too thin and additional milk or cream if it is too thick.

Remove cake from the fridge and frost with the chocolate frosting. Smooth the edges of your cake with an offset spatula—this will help your caramel drip down the sides nicely. Refrigerate your cake and the leftover for at least three hours (or overnight), until the frosting is set.

When your frosting has set, warm the caramel sauce just until it is thin enough to drip down the sides of your cake. Transfer it to a squeeze bottle and squeeze caramel around the top edge of your cake. Squeeze the bottle a little harder in some places to create drips, then fill in the circle with the remaining caramel sauce. Refrigerate to set the caramel, then slice and serve.