1. Place a rack in the center of the oven. Preheat the oven to 350°F. Grease and flour a 9-inch spring-form pan. Tap out the excess flour. Place the pan on a 12-inch square of heavy-duty aluminum foil. Mold the foil tightly around the base and about 2 inches up the sides of the pan so that water cannot seep in.

2. In a medium bowl, stir together the sugar, flour, and cinnamon.

3. In a large mixing bowl, whisk the ricotta until smooth. Beat in the eggs, vanilla, and lemon zest until well blended. (For a smoother texture, beat the ingredients with an electric mixer or process them in a food processor.) Whisk in the dry ingredients just until blended.

4. Pour the batter into the prepared pan. Set the pan in a large roasting pan and place it in the oven. Carefully pour hot water to a depth of 1 inch in the roasting pan. Bake 1½ hours or until the top of the cake is golden and a toothpick inserted 2 inches from the center comes out clean.

5. Turn off the oven and prop the door open slightly. Let the cake cool in the turned off oven 30 minutes. Remove the cake from the oven and remove the foil wrapping. Cool to room temperature in the pan on a wire rack.

6. Serve at room temperature or refrigerate and serve slightly chilled. Store covered with an inverted bowl in the refrigerator up to 3 days.