Use your fingers to butter 2 1/2-inch muffin tins, and then coat each one generously with Graham cracker crumbs. Set aside. Separate 3 eggs, placing the whites in one mixing bowl and the yolks in another. Now, beat the 3 egg whites until stiff, and set aside. Bet the 3 egg yolks just slightly. In a large mixing bowl combine the 3 beaten egg yolks, 3/4 cup sugar, and (2) 8 oz. packages of softened cream cheese. Beat until smooth and fluffy. Now, fold the 3 stiffly beaten egg whites into the the creamy mixture. Blend gently, but completely. Spoon cheesecake mixture into prepared muffin tins, filling 3/4 full. Bake at 350 degrees for about 15 to 20 minutes. The cheesecakes will be pulling away from the sides of the muffin tin and will be beginning to brown just a little. Allow baked cheesecakes to cool 10 to 15 minutes. The centers will fall, forming an indentation on each cheesecake. Carefully remove the miniature cheesecakes from the muffin tins, keeping as much "crust" intact as possible, and place on a nice serving plate. Spoon about 1 teaspoon of the Sour Cream Filling (below) into each indentation. Store, covered with plastic wrap, in the refrigerator until ready to serve.