Prepare the cheesecake layer first. This can be done early in the day or the night before. If freezing the cheesecake, it can be stored 1-2 weeks in the freezer.
Preheat oven to 325 degrees F. Using a large roasting pan, add 1 inch of water to the pan and place it on the lower 2/3 of the oven. Allow it to preheat.
Prepare the 9-inch springform pan by wrapping the bottom (outside) with a double layer of foil and lining the bottom (inside) with a circle of parchment paper.
Beat the 16 ounces softened cream cheese with 1 cup granulated sugar for 2-3 minutes until creamy, then add 1/4 teaspoon kosher salt and 2 large eggs, one at a time, beating well after each addition.
Beat in 1/4 cup sour cream and 1/3 cup heavy cream until light and fluffy (about 2 minutes). Pour into prepared springform pan, then place in center of the preheated roasting pan, being careful not to spill water.
Bake cheesecake for 45 minutes, then turn off the oven and let it sit for an additional 30 minutes. Remove and cool completely on the counter.
Once cooled, remove the outside portion of the springform pan and place in the freezer for several hours or overnight. If using within 24 hours, refrigerate instead.
For the carrot cake layers, preheat oven to 350 degrees F. Grease and flour two 9-inch cake pans and set aside.
In a large mixing bowl, combine 2 cups granulated sugar, 1 cup canola oil, and 4 large eggs until blended. Add 2 cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon baking powder, 1/4 teaspoon kosher salt, and 2 teaspoons ground cinnamon. Beat for about 2 minutes, then fold in 2 cups shredded carrots and pour into prepared cake pans.
Bake for 30 minutes, cool on wire rack for ten minutes, then remove from pans and cool completely.
For the frosting, combine 1 cup unsalted butter and 8 ounces softened cream cheese in a mixing bowl and beat with a whisk attachment for 3 minutes. Add 4 cups powdered sugar, 1 tablespoon vanilla extract, and 1/4 cup heavy cream, then beat for another 3-4 minutes until light and fluffy. Fold in 1 cup chopped pecans.
To assemble the cake, layer one layer of carrot cake on a serving plate, add the chilled or frozen cheesecake, then top with the second layer of carrot cake. Spread frosting on the sides and top, decorating with extra pecans if desired.
Store in the refrigerator, covered, for up to 3 days. ENJOY!