Slice the strawberries and place them in a medium bowl. Sprinkle with the sugar and toss to coat. Let sit on the counter for at least an hour to let the berries macerate the the juice to come out.
Once the berries have sat, add them and their juices to the blender, along with the basil leaves and puree until smooth.
Add 2 TB strawberry puree to each champagne or wine glass. Fill with ice and top with approximately 6 ounces sparkling water. Stir to combine and enjoy!
Notes
This is not meant to be overly sweet, but you may need to adjust the sugar depending on your preferences and how ripe your strawberries are.