1Mix butter,1/2 cup of the sugar and 1/2 teaspoon of the vanilla with electric mixer on medium speed until light and fluffy. Gradually add flour, mixing on low speed until blended. Press onto bottom of 13x9 inch pan. Bake at 350 degrees for 20 to 23 minutes or until lightly browned.
2Mix cream cheese, remaining 1/2 cup sugar and 1/2 teaspoon vanilla with electric mixer on medium speed until well blended. Add eggs; mix well. Blend in chips. Pour over crust. Dot top of cream cheese mixture with topping. Cut through batter with knife several times for marble effect. Bake at 350 degrees for 30 minutes. Cool in pan on wire rack. Cut into bars.