For the Cheesecake Layer 

1. Spray a 9-inch springform pan with nonstick spray, then line the bottom of the pan with parchment, then spray again.
2. In a large bowl, beat cream cheese, sugar, and eggs together until smooth. Beat in sour cream and heavy cream. Blend in salt and vanilla With the mixer on low speed. Mix well and pour the batter into the prepared 9-inch springform pan.
3. Bake in the preheated oven for 60 to 70 minutes, or until the center is almost set. Refrigerate at least 6 hours or overnight before removing from pan. 

For the Cake Layers: 

1. In a large bowl, cream butter and sugar together until light and fluffy. Beat in eggs one at a time, then stir in vanilla.
2. Sift flour, baking powder, and salt together in a separate bowl. Add flour mixture to butter mixture alternately with milk, mixing just until incorporated. Pour batter into 9 in round pans.
3. Divide  the cake batter into 2 separate bowls. Dye one with red gel and the other with blue. Pour into 2 9 in round pans. 
4. Bake in preheated oven for 40 to 45 minutes, or until a toothpick inserted into the center of the cake comes out clean. Let cool in pan for 10 minutes, then turn out onto a wire rack and cool completely.

To make the frosting:

1. In a large bowl, beat together the butter and cream cheese with a mixer on medium-high speed until pale and creamy, about 1 minute.
2. Reduce speed to medium. Add powdered sugar 1 cup at a time, beating well after each addition. Add salt, 3 tablespoons milk, and vanilla and beat until fluffy, about 3 minutes. Add an additional tablespoon of milk if you'd like the frosting to be more creamy.

To assemble the cake:

1. Place the red cake layer on a cake plate and spread a small amount of frosting on top. Remove the cheesecake from the pan and place the cheesecake layer on top of the red layer (be sure to measure it and make sure that it fits on top... you may need to place it on a cutting board and shave off some of the edge with a sharp knife to match the size of the cake layer). 
2. Spread frosting on top of the cheesecake layer. Add the blue layer on top. Scoop some frosting on top of the blue layer and cover the entire cake in a VERY THIN LAYER of frosting (you're just doing a "crumb coat.")
3. Then place the cake in the freezer for a few minutes, just until the cake and frosting are a little bit firm. Then add the remaining frosting to the top of the cake, spread across the top evenly and down the sides. Sprinkle festive sprinkles on top, if desired. The cake should be refrigerated until ready to serve.