Preheat the oven to 350ºF (180ºC).
Butter a 9-inch round cake pan with a removable bottom and dust with sugar, shaking off excess.
Mix ricotta, orange zest, and vanilla (if using) in a large bowl. You can beat this for a minute or so if you want a smoother texture. I don’t do it.
Add the flour, HALF the sugar, salt, and mix well.
Separate eggs, one by one, adding the yolks to the bowl with the ricotta mixture and the whites in another clean (very clean and dry, with no traces of oil or grease) bowl. I use the stand mixer for the whites and put them directly in the mixing bowl. Try using an extra small bowl for cracking each egg so you don’t risk the tiniest bit of yolk getting into the whites since it will prevent them from beating as they should.
Beat whites for 30 seconds and gradually add the remaining HALF of the sugar while beating at medium speed.
Keep on beating at high speed until it foams and triples in volume, but medium-soft peaks form when the beater is lifted.
Add the beaten egg whites to the ricotta mixture with a spatula in 3 parts, adding the next part after almost incorporating the last part. This way, you don't overmix the whites and they keep some volume.
After the third part is added, make sure the mixture is combined. Don’t overmix it so it rises well in the oven and has airy texture.
Put in the prepared pan, smoothing the surface, and bake for 50-55 minutes, or until it’s golden, but the center of the cheesecake still wiggles when lightly shaken, similar to brownies.
Remove from oven and let cool for 10 minutes on a wire rack, then run a smooth knife around the sides to ensure it is not stuck.
Let cool completely in the pan before transferring it to the serving plate. I like to wrap the pan in plastic and refrigerate the cheesecake for a few hours or until the next day before eating.