Preheat oven to 350F
Butter and flour a 10-inch springform cake pan, shaking off any excess.
Put the ricotta and sugar in a large bowl of a stand mixer (or use an electric hand mixer) and mix well until the sugar is all incorporated and the ricotta is smooth.
Fold in the egg whites thoroughly and pour the mixture into the buttered pan.
Bake until the top is golden brown and a thin knife inserted in the center of the cake comes out clean, 40 to 45 minutes.
Cool at room temperature, remove from the pan, sprinkle with confectioner’s sugar, and serve.