1. Process mango, sugar, and 1/2 cup plus 2 Tbsp. water in a blender 30 seconds to 1 minute or until smooth, stopping to scrape down sides. Pour mixture through a wire-mesh strainer into a medium bowl; discard solids. Cover and chill until ready to serve (up to 4 hours).
2. Spoon 3 Tbsp. mango puree into each of 6 Champagne flutes. Fill with Champagne; gently stir. Garnish, if desired. Serve immediately.