Margarita Punch

2 ounces frozen lemonade concentrate

12 ounces frozen limeade concentrate

1 cup powdered sugar

6 cups crushed ice

2 liters carbonated lemon-lime beverage

2 thinly sliced lime

Combine the concentrates, powdered sugar, and crushed ice in a large freezer proof container. Cover tightly and freeze for at least one hour (or for many days depending on how early you're planning ahead). Place the frozen mixture into a large punch bowl. Slowly pour in the soda and add the lime and/or lemon slices. Serve in chilled (salt rimmed optional) glasses.