In small saucepan, melt butter; stir in sugar until well mixed. Add 2 tsp. lemon peel. Pour into greased 9x13” pan. Arrange blueberries in a single layer over top; set aside. Prepare cake batter according to package directions, but omit 1/4 c. of the water and add 1/4 c. lemon juice and the remaining 2 tsp. lemon peel. Carefully pour over blueberries. Bake at 350 degrees for 30-35 minutes or until toothpick in- serted near center comes out clean. Cool. Serve with whipped cream if desired.