Grease a 9-inch (23 cm) springform pan with butter. For added ease of removal, I like to line the bottom with a circle of parchment paper as well.
Place a rack in the middle of your oven, then preheat to 325°F (163°C).
In a clean stand mixer bowl (or large non-reactive bowl with a hand mixer), beat the egg whites until they are firm and holding their shape, but not forming stiff peaks. Remove the egg whites from the bowl and set them aside.
(Optional) - For a smoother cake texture, blend the ricotta with the egg yolks before combining with the remaining cake ingredients.
In the same mixing bowl, combine the remaining cake ingredients. Mix with a paddle mixer (or hand mixer beaters) until well-combined (don't worry too much about small pieces of cream cheese that won't mix in).
Gently fold the whipped egg whites into the batter with a spatula. Pour the mixture into the greased springform and tap to level.
Drizzle a few tablespoons of the blueberry sauce onto the top of the batter (try to use the more liquidy portion of the sauce for this). You can drag a small knife through the sauce for added decorative effect, if you like.
Bake for 1 hour, or until browned at the edges and just barely set in the center. Turn off the heat and leave the cheesecake in the oven with the door closed for an additional 30 minutes. Remove the cake from the oven and cool on the counter for 10 minutes. Loosen the springform (run a knife around the outside if you're concerned about sticking). Allow the cake to cool completely, then chill in the fridge overnight.
Top the chilled cheesecake with the blueberry sauce, or serve individual slices with sauce on the top or the side.