Step 1

Make cantaloupe-basil simple syrup: Combine water, sugar, and ½ cup basil leaves in a small saucepan. Bring to a boil, stirring briefly just until the sugar dissolves. Remove from heat, set pan in a bowl of ice with a little water, and stir occasionally until syrup is completely cool, about 30 minutes. Strain syrup into a glass jar, pressing on basil with a spatula to release all of the flavor. Discard basil.

Step 2

Puree cantaloupe in a blender until very smooth. Stir in simple syrup and lime juice.

Step 3

For each drink, fill a glass with crushed ice and pour 1/2 cup cantaloupe mixture over it. Add 1 tablespoon gin (if using), and top with ¼ cup sparkling water or Prosecco. Garnish each glass with a cantaloupe wedge, lime slice, and a few basil leaves.