Foamy Pineapple Punch

1 (48 ounce) can chilled pineapple juice
6 tablespoons divided lemon juice
Ice cubes
1 (750 ml) bottle chilled champagne

For each serving, measure into blender, 1 cup pineapple juice, 1 tablespoon lemon juice and 1 cup ice cubes. Whirl until foamy. Pour into glass and add 1/2 cup champagne.