Preheat the oven to 325°F and line a loaf pan with parchment paper. Crush the graham crackers in a food processor or blender, then stir in the melted butter. Pour the graham cracker mixture into the loaf pan, then press it down into the bottom of the loaf pan using the base of a clean glass.
Beat the cream cheese with a hand mixer until smooth and creamy, then stir in the sugar. Add in the corn starch, eggs, and vanilla extract and stir everything together until combined. Pour the cheesecake batter over the graham cracker crust.
Cover the loaf pan with aluminum foil and place it in a large casserole dish. Heat some water in a kettle and pour it into the casserole dish in order to surround the loaf pan with water. Transfer the casserole dish to the oven and bake the cheesecake at 325°F for 75 minutes. Once it's done baking, take the loaf pan out of the casserole dish, remove the aluminum foil, and use the parchment paper to help lift the cheesecake out of the loaf pan. Let the cheesecake cool for about 2 hours.
While the cheesecake is cooling, line the loaf pan with some additional parchment paper and cover the bottom with soft caramels. Transfer the loaf pan to the oven and let the soft caramels melt in the residual heat of the oven for about 5 minutes. Remove the loaf pan from the oven and let the caramel layer cool and solidify.
Beat the butter and dark chocolate sauce or spread with a hand mixer until the mixture becomes light and fluffy, then stir in the sweetened condensed milk. Place the caramel layer on top of the cheesecake, then frost the cheesecake with the chocolate buttercream frosting. Make a series of ripples in the chocolate buttercream frosting on top of the cheesecake to make it look like a giant Twix bar.
