3 cups sifted powdered sugar (sift, and then measure)
Preheat the oven to 325 degrees F and set a kettle of water to boil.
Grease a 9″ springform pan, and line the bottom with a round of parchment paper. Wrap the outside of the pan with heavy duty aluminum foil, and set the pan into a larger pan (for the waterbath.)
In the bowl of a mixer, beat the cream cheese on medium until fluffy. Add the sugar and beat until smooth. Switch to a wooden spoon and beat in the lemon zest, lemon juice, and salt. Add eggs one at a time, making sure they are combined but not overmixing. Add the sour cream. Stir in flour and gently mix just until combined.
Pour the batter into the greased pan. Pour boiling water into the larger pan halfway up the cheesecake. The aluminum foil should protect the cheesecake from seeping water. Bake until the cheesecake is just set in the middle, about 40 minutes. Run a knife around the sides and let the cheesecake cool completely. Press plastic wrap onto the surface of the cheesecake and refrigerate overnight.
(I made the cake the day after I made the cheesecake, so it had rested overnight in the fridge and was sturdy enough to flip.)
For the red velvet, preheat the oven to 350 degrees F. Grease and flour two 9″ pans.
Sift the flour, sugar, baking soda, cocoa powder, and salt together in a medium bowl. In the bowl of a mixer, beat the eggs, oil, buttermilk, vanilla extract, and vinegar until well combined. Add the dry ingredients and as much food coloring as you like. Beat until well combined, about two minutes.
Divide the batter between the two pans. Bake 25-30 minutes, rotating the pans halfway, or until a toothpick comes out clean. Cool the cakes in the pans for five minutes, then run a knife around the edges. Invert them onto cooling racks and cool completely. (I like to make the frosting at this point, while the cakes cool down.)
Cream Cheese Frosting
Beat the cream cheese and butter in an electric mixer until very smooth and lump-free. Beat in the vanilla and almond extracts. Then stir in the powdered sugar a cup at a time until very smooth.
Assembling the cake.
Use a cake leveler or serrated knife to level the tops of the red velvet cakes. Put one of the layers, cut-side up and parchment paper removed, on a serving plate. Spread with a very small amount of frosting, just enough to cover the cake in a thin layer.
Take the cheesecake out of the fridge. Open up the springform pan and peel off the plastic wrap. The cake should be pretty sturdy. My cheesecake was still attached to the bottom of the springform pan. I simply used one hand to hold it, and gently flipped it over onto the red velvet. I lifted off the bottom of the springform pan and peeled off the parchment paper. Piece of cake.
My cheesecake was wider than the red velvet. I just gently sawed a knife around the edges and trimmed the excess.
Spread another very thin layer of frosting on the top of the cheesecake. Flip the remaining layer of red velvet, cut side down, on top. Peel off the parchment paper.
Use about a third of the cream cheese frosting to cover the whole cake with a crumb coat. Basically, you want to frost the cake with as little frosting as possible, picking up all the red crumbs and sealing the cake. Refrigerate the cake for half an hour, or until the crumb coat is hardened.
Then frost the cake with the rest of the cream cheese frosting. I decorated mine with white chocolate shavings.