2PREPARE THE BATTER: Place the egg yolks in a food processor for 5 seconds then add the cream cheese and beat until smooth.
3Add the brown sugar and vanilla and process for several minutes, or until the batter is very smooth.
4Beat the egg whites and fold into the cheese mixture; set aside.
5PREPARE THE CRUST: Soften butter and combine with graham cracker crumbs; mix until fully blended, e.g. they will form a ball when squeezed in your hand or by a spoon.
6Pat the crust into the sides and bottom of a springform pan about 9 inches in diameter; spread a generous layer of chips on the bottom of the pan and then pour the batter into the pan.
7Add another generous layer of chips to the top of the cake, then place the filled pan into the preheated oven.
8Baking time will vary from about 30 minutes to 2 hours; cooking time depends on whether you want a soft, gooey "New York" style cheesecake (shorter) to a fluffy "souffle" like cheesecake (longer) - the longer you cook it, the fluffier it gets.
9When the cake starts to rise like a souffle, start checking to see if it is done; it will just about double in volume and should not flow over the sides of the pan.
10TIPS: If the cake shimmers like gelatin when shaken, it is done; Alternatively, if a knife inserted comes out clean, the cake is overcooked: the knife should be very lightly coated with batter.