Preheat oven to 350 degrees.
Spray a 9 or 10" springform pan with cooking spray and cover the bottom with parchment paper.
Blend the egg yolks and sugar in food processor until thick and pale (about 1/2 minute). Add the ricotta, flour, sour cream (or mascarpone), zest and cinnamon. Blend another 30 seconds.
Beat egg whites with the salt in a large bowl until they hold stiff peaks. Pour ricotta mixture gently down the side of the bowl. Fold in gently but thoroughly.
Gently pour the batter into the springform pan. Set on a baking sheet to catch any stray drips. Bake 35-45 minutes. Center should be set and spring back to your touch. Run a knife around the outside edge of the cheese cake as soon as you remove it from the oven.
Transfer pan to a rack to cool. After 30 minutes remove sides of pan. Loosen the bottom and slide the cake carefully to serving platter. (you can leave the parchment paper on the bottom).
Sprinkle with icing sugar and serve warm or at room temperature.
Tradition is to serve this cake the day it is made but you can make it one day ahead, cool uncovered, then chill covered. Serve the next day.