For the Crust: Preheat oven to 350 degrees F. Grease the inside of a 9 inch spring form pan with butter. Lay two large pieces of aluminum foil crosswise on your work surface. Place the cake pan in the middle and crimp the aluminum around the pan.
Stir the crust ingredients together in a medium bowl. Once fully incorporated press into the bottom and sides of the prepared spring form pan, creating an even layer.
For the Chocolate Layer: Melt the chocolate over a double boiler or in the microwave. Pour over the prepared pretzel crust. Transfer the spring form pan to the refrigerate for 5 minutes or until chocolate has set.
For the Filling: Whip together the cream cheese and sugar until fluffy. Add the sour cream, eggs, egg yolk, vanilla and salt and stir together until incorporated. Do not over mix to avoid excess air from being incorporated into the mixture which can cause your cheesecake to crack when baking. Pour the filling over the prepared crust and chocolate layer.
Transfer the cake to a roasting pan and carefully fill the roasting pan with warm water until it comes 1/3 of the way up the sides of the spring form pan. Bake in the preheated oven for 50 to 60 minutes or until the center only jiggles slightly. Remove and allow to cool on a wire rack for 20 minutes.
For the Caramel Sauce: Mix the sugar and water in a small sauce pot just to wet the sugar. Place over medium-high heat and cook until the mixture turns a light golden brown or a candy thermometer reads 212 degrees F.
Remove the pan from the heat and add the butter, heavy cream, and salt. Be careful the mixture may bubbly rapidly. Stir the mixture until fully incorporated. Allow to cool for 3 minutes before pouring over the cheesecake. Place the entire cheesecake into the refrigerator and allow to cool completely, at least 2 hours or until ready to serve. Use a warm knife to cut through the cake.