At least 4 hours ahead, layer the lemon slices and berries in a bundt pan or ring mold, cover with 2 cups water, and freeze solid.

In a large punch bowl or gallon pitcher, combine the pink lemonade and vodka and stir until fully blended.

Cover and refrigerate for at least 1 hour so the punch is properly cold before guests arrive.

Just before serving, pour in the chilled lemon-lime soda and stir once, gently, to keep the fizz.

Unmold the ice ring (run warm water over the back of the pan for a few seconds if it sticks) and float it in the bowl.

Ladle into punch cups, about 4 ounces each, and serve right away.