Place 2 to 3 dashes of orange bitters in each of 6 Champagne flutes or glasses. Add 1 Tbsp. lemon liqueur to each, and stir. Top each with Champagne or sparkling wine; garnish with lemon rind twist, if desired.
Tip: No lemon liqueur? Whisk together 1/3 cup fresh lemon juice and 1/4 cup powdered sugar instead.