Place a piece of plastic wrap, lightly coated with nonstick spray, on top of the cheesecake. Set the 9 inch cake pan, bottom side down, on top of the cake. Invert the cake together with the pan and set the pan on a counter. Remove the springform pan bottom and the parchment and blot any moisture from the cake with a paper towel. Wash and dry the pan bottom.
Using a small offset spatula, spread about 3 tablespoons of the raspberry preserves onto the bottom of the cheesecake.
Transfer the red velvet cake, top side up, to a cutting board. If the cake is not perfectly flat, use a long serrated knife or a cake leveler to get it to ¾ in high. You want the cake in a 9 inch disk. You can use the springform pans bottom for a reference.
Reinvert the cake, using two large pancake turners, set the red velvet cake on top of the cheesecake. Position the cake so that the sides are flush with the cheesecake's sides. Place a serving plate on top of the cake. Slip the palm of your hand under the 9 inch cake pan and holding the bottom of the serving plate with your other hand, quickly reinvert the cake.
Slide a few wide strips of parchment under the cake to keep the rim of the plate clean. Carefully spread as much of the remaining raspberry preserves as necessary onto the sides of the red velvet cake to seal in the crumbs. Slide out the parchment strips and use a paper towel to wipe any preserves from the serving plate. Slide a clean set of parchment strips under the cake and carefully apply a thin layer of buttercream to the red velvet cake as an undercoat. Wipe off any red-tinted frosting from the spatula before frosting the rest of the cake.
Refrigerate the cake for 10 minutes to firm up the undercoat. Use the remainder of the buttercream to frost the top of the cake, Work quickly because the cold cheesecake will cause the buttercream to set. Slowly, slide the parchment strips out from under the cake/
If desired, pipe a border of stars or shells around the edge of the cake.
Refrigerate for a minimum of 20 minutes to firm up the buttercream. Carefully spoon the prepared blueberry topping onto the top of the cake and arrange them in a single layer.
Refrigerate the cake until about 40 minutes before serving time. Run a knife blade under hot water and wipe it dry between each cut. This makes it possible to cut through the firm buttercream and keeps the red from the red velvet cake from staining the ivory color of the cheesecake. Let the slices soften for 20-30 minutes at room temperature before serving.