
Heat oven to 350°. Butter and flour a 9-inch spring form pan.
Make ricotta batter:
2 eggs
¼ cup sugar
½ teaspoon vanilla
15 oz. ricotta cheese
In a small mixing bowl, beat two eggs with ¼ cup sugar until doubled in volume and mixture is light and pale yellow, about three minutes. Stir in the vanilla and then beat in the ricotta until just smooth. Set aside.
Make cake batter:
6 Tablespoons soft unsalted butter
½ cup sugar
2 eggs, separated
3/4 cup buttermilk (or milk)
1½ cups cake flour
½ teaspoon kosher salt
2 teaspoons baking powder
Zest of one lemon
Cream the butter and ½ cup sugar together in a large mixing bowl until smooth and creamy. Add 2 egg yolks, beat well. Stir in the buttermilk. Sift together the cake flour, salt and baking powder and stir the flour mixture into the cake batter. Mix until just blended. In a small clean bowl, using clean beaters, whip the 2 egg whites until they are stiff and hold firm peaks. Fold the egg whites and lemon zest into the cake batter. Carefully stir until incorporated.
Pour the cake batter into the bottom of the spring form pan. Use a spatula to smooth the top. Give the ricotta mixture a quick stir with a clean spatula and pour the ricotta mixture over the cake batter. Smooth the top with the back of a spatula. Place the filled cake pan on a baking sheet and bake for about 55 minutes, or until the top is just cooked through at the center, turning once after 30 minutes so the cake browns evenly. Remove cake from oven to a wire rack. Let rest five minutes, then carefully loosen the hinge on the spring form pan. Run a knife around the edge if cake wants to stick. Remove ring and let cake cool completely.
