Heat the oven to 325 degrees. Place a 13 x 9-inch baking pan half filled with water on the bottom rack of the oven. In a medium mixing bowl, stir together the graham cracker crumbs, ¼ cup sugar, lemon zest, and melted butter until well mixed. Pat the crust mixture on the bottom and 1-inch up side of a 9-inch spring-form pan with a removable bottom. Using heavy duty foil, wrap the bottom and sides of the cheesecake pan with foil; set aside. In a large mixer bowl beat together the cream cheese, 1 cup sour cream, 1 cup sugar, flour, vanilla, and salt at medium speed until smooth and creamy (1 to 2 minutes). Add the eggs, one at a time, beating 10 to 15 seconds after each addition. Do not overbeat. Add the lemon juice, beating on low speed, just until mixed (10 to 15 seconds). Pour the batter into the prepared spring-form pan. Place the cheesecake on the middle rack above the pan of water. Bake until the sides of the cheesecake are set and the center is jiggly, but not wet (50 to 60 minutes). DO NOT OVERBAKE or the cheesecake will crack. Turn off the oven. Prop open the oven door with a wooden spoon. Leave the cheesecake in the oven for one hour. Remove from the oven and carefully rim the sides of the pan to loosen the cheesecake. In a small bowl stir together ¾ cup sour cream and the remaining 1 tablespoon of sugar. Spread the sour cream mixture on the top of the cheesecake. Place in the refrigerator for 6 to 24 hours, until completely cooled. Remove the sides of the spring-foam pan. Cut the cheesecake into pieces and serve. Refrigerate leftovers.