Step 1In a large bowl, combine the graham cracker crumbs and sugar. Stir in the butter until fully incorporated. Firmly press the mixture into the bottom of a greased 8-inch square baking dish.
Step 1Heat the oven to 300 degrees.
Step 2In a large mixing bowl, beat the cream cheese until it is soft and fluffy. Beat in the sugar, vanilla and lemon zest until fully combined. Beat in the eggs, one at a time, then fold in the sour cream until blended. This makes about 3 1/2 cups filling.
Step 3Pour the mixture over the pressed graham cracker crust in the dish, and sprinkle the chocolate chips over the top. Bake the cheesecake until it is set and jiggles slightly when tapped (as with gelatin), about 45 to 55 minutes. Turn off the oven, leaving the cheesecake in the oven to cool. Remove the cooled cake and refrigerate overnight before serving.