Preheat oven to 325 degrees. Set a kettle of water to boil. Using an electric mixer, beat cream cheese on medium until fluffy, scraping down side of bowl.
Gradually add sugar, beating until fluffy. Beat in lemon zest and juice, and salt.
Beat in eggs, one at a time, scraping down side of bowl after each addition.
Beat in sour cream.
Cut parchment paper in a circle and line the bottom of the cheesecake pan. Wrap bottom half of pan in foil. Pour in filling; place in a roasting pan. Pour in boiling water to come halfway up side of springform. Bake until just set in center, about 45 minutes. Remove pan from water; let cool 20 minutes. Run a paring knife around edge; let cool completely. Cover; chill overnight, then wrap in plastic wrap and freeze.
For the cake:.
Preheat oven to 350°. Sift together flour, sugar, baking soda, cocoa, and salt into a medium bowl.
Beat eggs, oil, buttermilk, food coloring, vanilla, and vinegar in a large bowl with an electric mixer until well combined.
Add dry ingredients and beat until smooth, about 2 minutes.
Divide batter evenly between 2 greased and floured 9" round cake pans and bake 25-30 minutes, rotating halfway through, until a toothpick inserted in the center of each cake comes out clean. Let cakes cool 5 minutes, then invert each onto a plate, then invert again onto a cooling rack. Let cakes cool completely, then level.
Beat cream cheese, butter, and vanilla together in a large bowl with an electric mixer until combined.
Add sugar and beat until frosting is light and fluffy, 5–7 minutes.
Place bottom cake layer on cake stand. Remove cheesecake from freezer, unwrap, and remove from metal bottom, then peel off parchment paper. Place cheesecake layer on top of the bottom layer of the red velvet cake. If the cheesecake is wider than the cake, and it is necessary to to trim it, wait approximately 10 minutes for the cheesecake to soften, then trim it with a knife. Place top layer of cake on top of the cheesecake, and coat with a generous layer of the cream cheese frosting to act as the crumb coat. Be careful not to get any red velvet crumbs in the bowl of frosting!
Refrigerate approximately 30 minutes, then frost with as much of the remaining frosting as necessary.
Top with shaved white chocolate and/or shaved dark chocolate. Refrigerate until ready to serve. (This cake doesn't have to stay in the fridge until immediately before serving - it's fine to let sit out 20-30 minutes!).