PREHEAT oven to 350°F. Grease 13x9-inch baking pan; set aside. Beat cake mix, pumpkin, dressing and eggs in large bowl with electric mixer on medium speed until well blended. Pour into prepared pan
BAKE 32 to 35 min. or until wooden toothpick inserted in centre comes out clean. Cool completely on wire rack.
BEAT cream cheese, butter, milk and vanilla in large bowl with electric mixer on medium speed until well blended. Gradually add sugar, beating after each addition until well blended. Spread over cooled cake. Cut into pieces to serve. Store any leftover bars in refrigerator.