Preheat your oven to 375 degrees F. Spray three 8-inch or four 6-inch round cake pans with non-stick spray and then line with parchment. Spray again. Set aside.

In a medium sized bowl combine the pretzel crumbs, melted butter and brown sugar. Stir until all the pretzel crumbs are damped by the melted butter.

Divide evenly between the pans and press down firmly with your hand or the back of a spoon.

Bake for 8-10 minutes, until golden brown. Let cool while you make the chocolate cake batter.

Preheat the oven to 350 degrees F. 

Combine the flour, sugar, cocoa, baking soda, baking powder, and salt into the bowl of an electric mixer fitted with a paddle attachment and mix on low speed until combined.

In another bowl, combine the buttermilk, oil, eggs, water and vanilla.

With the mixer on low speed, slowly add the wet ingredients to the dry, scraping the bottom of the bowl with a rubber spatula.

Pour the batter into the prepared pans (about 15 ounces in each 8-inch pan or 12 oz in each 6-inch pan), over the cooked pretzel crusts and bake for 18-20 minutes, until a toothpick inserted in the center of the cake comes out with a few moist crumbs on it.

Cool in the pans for 10 minutes, then turn them out onto a cooling rack and cool completely.

Wrap in plastic wrap and chill in the freezer until ready to use. Do not chill in your refrigerator. The crust will get soggy.

Preheat your oven to 300 degrees F. Line the bottom of a 6x6-inch baking pan with plastic wrap (I know, it sounds crazy but it won't melt). Set aside.

In a stand mixer fitted with a paddle attachment mix the cream cheese on low speed for about 2 minutes. Scrape down the sides of the bowl with a spatula and add the sugar and mix for another 1 to 2 minutes, until the sugar has been completely incorporated. Stop the mixer and scrape down the sides of the bowl.

In a small bowl, whisk the cornstarch and salt until combined. In a slow and steady stream, whisk in the milk and then the egg until the mixture is homogenous.

With the stand mixer on medium-low speed, stream in the egg mixture. Mix for 3 to 4 minutes, until the mixture is loose. Scrape down the sides of the bowl and mix for another 30 seconds.

Pour the cheesecake batter into the prepared pan and bake for 20 minutes. Gently shake the pan. The cheesecake should be firm and more set toward the rim of the baking pan but still a little loose in the dead center. If the cheesecake is still jiggly all over, give it another 5 minutes and 5 more if it needs it. If it begins to brown, take it out of the oven immediately.

Let cool to room temperature and transfer to a medium sized bowl. Fold in the chocolate chips. Cover and refrigerate overnight.

In a microwave safe bowl, heat the cream and then pour it over the chocolate to melt. Stir until the mixture is smooth and silky. If needed heat the mixture for another 20 to 30 seconds and stir until the chips are melted. Set aside.

In a stand mixer fitted with the paddle attachment, beat the butter on medium speed for one minute. 

Turn the mixer to medium-low and gradually add the melted chocolate ganache. Stop the mixer and scrape down the sides of the bowl. Beat again for about one minute.

Gradually add the powdered sugar.

Add the vanilla and salt and beat for about 5 minutes.

Using a wooden spoon, mix the frosting by hand, trying to push out any air bubbles.

Level the chocolate cakes as needed.

Spread a little frosting on a cake board and place the first cake layer, pretzel side down, on the cake board. 

Pipe a rim of frosting around the cake layer and fill with half of the chocolate chip cheesecake filling.

Place the next cake layer, pretzel side down, on top of the filling and repeat step 2.

Place the final cake layer, pretzel side down, on top of the second layer of filling and apply a thin crumb coat and refrigerate for 15 minutes.

Continue frosting and decorating with the remaining chocolate buttercream. Best served right away or day of. If you're not serving day of, place the cake in an air-tight container and freeze it over night. Bring it to room temperature before serving.