PREHEAT oven to 350º F. Tightly wrap outside bottom and side of 9-inch springform pan with 2 pieces of foil to prevent leakage.
MICROWAVE 1 1/4 cups morsels in small, uncovered, microwave-safe bowl on MEDIUM-HIGH (70%) power for 1 minute; STIR. Morsels may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until smooth. Cool to room temperature.
COMBINE crumbs, 2 tablespoons granulated sugar and butter in ungreased 9-inch-springform pan. Press onto bottom and 1-inch up side of pan.
BEAT cream cheese, remaining 1 cup sugar, sour cream and vanilla extract in large mixer bowl until creamy. Add eggs, one at a time, beating well after each addition. Beat in melted chocolate until blended. Pour onto crust. Place pan in large roasting pan; fill roasting pan with hot water to 1-inch depth.
BAKE for 45 to 50 minutes or until edges are set but center still moves slightly. Remove cheesecake from water bath to wire rack. Run wet knife around edge of cheesecake. Refrigerate for 1 hour and remove side of pan.
MICROWAVE remaining morsels and whipping cream in small, uncovered microwave-safe bowl on MEDIUM-HIGH (70%) power for 1 to 2 minutes; STIR. If necessary, microwave at additional 10- to 15-second intervals, stirring just until smooth; cool for 5 minutes. Spread over cheesecake. Refrigerate for 4 hours or overnight.