Preheat the oven to 350F.

In a medium bowl, add graham cracker crumbs, butter, sugar, and salt. Stir to combine well. Add the mixture into the base of a 9-inch springform pan and use your fingers to press evenly into the bottom and halfway up the sides of the pan. Bake the crust for 10 minutes. Room from the oven and let cool at room temperature.

Reduce the oven temperature to 325F.

In a large bowl, add cream cheese, mascarpone, and granulated sugar. Using an electric mixer, beat to combine well. Add sour cream, heavy cream, flour, corn starch, salt, lemon zest, and vanilla extract. Continue to mix until everything is fully combined and the texture is soft and creamy, about four to five minutes. Add the eggs one at a time, mixing for one minute between each egg until the mixture is smooth.

Wrap the outside of the springform pan with two large pieces of aluminum foil so the bottom and sides are covered. Pour the cheesecake mixture into the springform pan. Tap the pan firmly on the counter 4 to 5 times to release any air bubbles that may be trapped. Place the springform pan in a larger baking dish and fill the baking dish with 1-1 ½ inches of hot water. Carefully place in the oven and bake for 1 hour and 25-30 minutes until the cheesecake is almost fully set, with a slight jiggle in the middle. If the cheesecake top begins to cook too quickly, add a piece of aluminum foil over the top while baking.

Remove the cheesecake from the oven and carefully remove the springform pan from the baking dish. Allow the cheesecake to fully cool on a cooling rack at room temperature. Then place in the fridge and let cool for at least 3-4 hours or overnight.

In a medium pan over medium heat, add the orange and lemon juice. Meanwhile, in a small bowl, mix together 3 tsp corn starch and 3 tsp water until the corn starch is fully dissolved and set aside. In a separate small bowl, add the sugar and orange and lemon zest and massage with your fingers to release the citrus oils. Add the eggs into the citrus sugar and beat until the mixture is light and foamy.

Once the juice on the stove is just about to boil, slowly add the hot juice ¼ cup at a time into the egg mixture, whisking the mixture constantly to avoid curdling. Repeat with an additional ¼ cup of juice. Pour the egg mixture into the pan on the stove while whisking constantly. Allow the mixture to come to a boil over medium heat, continuing to whisk. Add the corn starch mixture into the pan and whisk until fully combined. Cook for 2-3 minutes until the mixture has thickened lightly. Remove from the heat and add lemon extract and butter and whisk until smooth. Let sit until room temperature and then cool in the fridge for 1 to 2 hours until thickened.

Remove the cheesecake from the fridge and carefully remove the springform sides. Pour the citrus sauce over the top. To cut, place a sharp knife in very hot water to warm the blade before slicing, repeating as necessary to ensure clean cuts. Serve immediately.

Bon appetit!