in pan on rack. Reduce oven temperature to 325 degrees F. FOR FILLING: Using electric mixer, beat room temperature cream cheese and brown sugar in large bowl until smooth. Add peanut butter and vanilla extract and beat just until blended. Add eggs 1 at a time, beating just until blended after each addition. Add whipping cream and beat until smooth. Stir in peanut butter cup pieces. Pour filling into crust. Bake until sides of cake are set but center still moves slightly, about 55 minutes. Cool cake in pan on rack 10 minutes. FOR TOPPING: Blend sour cream, sugar and vanilla extract in medium bowl. Carefully spoon topping over cheesecake. Return cheesecake to oven and bake 5 minutes. Cool cheesecake in pan on rack. Run small sharp knife around edge of cheesecake to loosen. Cover and refrigerate overnight. (Can be prepared 3 days ahead. Keep refrigerated.) Release pan sides. Let stand 20 minutes at room temperature before serving. *