Preheat oven to 350 degrees F (180 degrees C) and butter, or spray with non stick cooking spray, a 9 inch (23 cm) spring form pan. Wrap the outside of the pan with two layers of heavy aluminum foil. 

For Crust: In a medium sized bowl combine the graham cracker crumbs, sugar, and melted butter. Press the crumbs evenly over the bottom of the spring form pan. Cover and refrigerate while you make the filling.

For Filling: In the bowl of your food processor or electric mixer (or hand mixer), place the cream cheese and beat until smooth and free of lumps. Add the ricotta and sugar and beat until smooth (about 2 - 3 minutes), scraping down the bowl as needed. Beat in the cornstarch. Add the eggs, one at a time, beating about 30 seconds after each addition. Scrape down the sides of the bowl. Beat in the lemon zest and vanilla extract, and beat until incorporated. 

Remove the crust from the refrigerator and pour in the filling. Place the spring form pan in a large roasting pan. Pour enough hot water into the roasting pan to come about halfway up the sides of your spring form pan. 

Bake for about one hour to one hour 15 minutes, or until the top of the cheesecake has nicely browned and the center of the cake moves slightly when the pan is gently shaken. Remove the pan from the water bath and cool on a wire rack. Cover and refrigerate until the cheesecake is cold, about 6 - 8 hours or overnight. Serve in small slices with a spoonful of Cran-Raspberry Sauce (if desired).

Cran-Raspberry Sauce: In a large saucepan combine all the ingredients. Cook over medium heat, stirring often, until the sauce thickens and is bubbly. Remove from heat and add zest of one lemon or orange, if desired. Let cool. (Note: taste and add more sugar as needed.) Cover and store in the refrigerator. Makes about 2 cups (480 ml).

Note: Place the ricotta in a fine-meshed strainer or else a cheesecloth-lined strainer that has been suspended over a bowl. Cover and place in the refrigerator to drain for several hours, or even overnight.