Preheat oven to 350 degrees F (175 degrees C). Grease a 9 inch springform pan.
In a medium bowl, mix together the graham cracker crumbs, 3 tablespoons of sugar and melted butter. Press onto the bottom and up the sides of the springform pan.
In a large bowl, beat together cream cheese and ricotta cheese until smooth. Beat in sugar and flour. Add eggs one at a time, beating well after each addition. Stir in salt, vanilla extract and lemon zest.
Pour filling into prepared crust. Bake in preheated oven for 55 to 60 minutes. Let cool before serving.