1. Stir sugar and 1/2 cup water in heavy small saucepan over medium-low heat until sugar dissolves. Increase heat and bring to a boil. Cool syrup. 2. Divide strawberries among 6 glasses (6-8 ounces each); add 1 tablespoon syrup to each and mash with muddler or handle of a wooden spoon. Add a lemon slice to each and mash to release flavor. Add several ice cubes to each glass and then fill with Prosecco.
