Put the chocolate chips in a small microwave-safe bowl. Heat in microwave oven at 100 percent power for 40 seconds or until melted. Or, gently melt chocolate in small, heavy saucepan over very low heat. Stir melted chocolate into reserved 1/2 cup filling. Spoon in dollops, evenly spaced, over top of filling in springform pan. With the tip of a small knife, swirl chocolate dollops into white batter to marbleize, being careful not to hit bottom crust. Place springform pan in large baking pan on oven rack. Pour enough boiling water into large pan to come halfway up sides of springform pan.