Melt butter in an 8 inch square pan. Sprinkle sugar evenly over butter. Mix blueberries and 1 teaspoon lemon peel; sprinkle over sugar.
Prepare yellow cake mix according to package directions, stirring in 1 teaspoon lemon peel at end of mixing. Spread batter over berries.
Bake in a moderate oven (375 degrees) for 30 minutes or until cake tests done. Let stand for 10 minutes. Turn out onto platter. Serve warm. Top with whipped cream at the table if you wish. Serves 9.