Spray three 8-inch round cake with nonstick spray, line the bottom with parchment paper, and spray again. Set aside.

Mix together the finely ground pretzels, graham cracker crumbs, melted butter and granulated sugar. Stir until the mixture resembles "wet sand."

Evenly divide the crumbs between the three cake pans (about 8 ounces in each). Firmly press the crumbs onto the bottom of each pan to create a crust.

Set aside.

Preheat your oven to 325 degrees F.

In a medium size mixing bowl, whisk the cake flour, dark cocoa powder, and salt to combine. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugars on medium-high until light in color and fluffy in texture, about 3 minutes.

With the mixer on medium speed, add the eggs one at a time, making sure to scrape down the sides and bottom of the bowl between each addition. Continue to beat on medium-high speed for about 2 minutes, until smooth. Add the vanilla and stir to combine.

Turn the mixer to low speed and add 1/3 of the flour mixture to the butter mixture. Mix until just incorporated and then add half of the buttermilk, followed by another 1/3 of the flour mixture, the second half of the buttermilk and lastly, add the remaining flour mixture and mix until just incorporated.

In a small bowl, combine the vinegar and baking soda. The mixture will bubble. Add the mixture to the cake batter and stir on low until combined. Scrape down the sides of the bowl and mix again for another 20 seconds.

Gently fold in the sour cream.

Divide the batter evenly between the prepared pans with the pretzel crust (about 20 ounces in each pan) and bake for about 35 to 40 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs on it. Reminder: we’re baking the cake and pretzel crust together.

Remove the cake pans from the oven and let the layers cool in pans for 15 minutes before inverting onto cooling racks to cool completely.

In a medium size bowl, combine the peanut butter and cream cheese and mix until combined. Mixture will be slightly thick. Set aside.

In a stainless steel bowl, beat the whipping cream, powdered sugar and vanilla on medium-high speed until still peaks form.

Mix sugar, water and corn syrup in a small saucepan.

Bring the water and sugar mixture to boil over medium heat, but DO NOT STIR. (Stirring encourages crystallization). Let the mixture cook until it caramelizes into a golden brown color. It happens quickly, so keep an eye on it.

Remove the caramelized sugar syrup from the heat and slowly mix in the cream. Pour in just a tiny bit at a time, especially at the beginning, and mix to combine. You can start adding more and more as you go along.

In the bowl of an electric mixer beat the butter on medium-high for 3 to 5 minutes.

Turn the mixer to medium and gradually add the caramel. Scrape down the sides of the bowl and mix again until the caramel is incorporated.

On low speed, gradually add the powdered sugar. Increase the speed to medium-high and beat for another 5 minutes, until light and fluffy.

Remember to mix the frosting by hand with a wooden spoon or large spatula to push out the air to create a silky-smooth frosting.

Place the first cake layer on a cake board, crust side down, on your cake board or cake stand. Pipe a rim of caramel buttercream around the edge of the cake.

Fill the center with 1 cup of the peanut butter pie filling.

Top with chopped peanuts, peanut butter cups and a generous drizzle of caramel.

Place the second cake layer on top and repeat these steps.

Place the final cake layer, top side down, on the second layer of filling.

Apply a thin coat of caramel buttercream around the entire cake to lock in the crumbs. Freeze for about 10 to 15 minutes.

After the crumb coat is set, continue frosting and decorating the cake with remaining buttercream. Use any remaining fillings as part of your toppings.