Loosely based on the French 75, a classic cocktail of gin, Champagne, lemon juice, and sugar, this sparkling beverage uses lemonade concentrate as a shortcut. Be sure to allow the concentrate to thaw ahead of time. You'll use almost a whole bottle of Champagne; the rest goes into the dessert. If time allows, you can use a quick simple syrup with lemon juice: Combine 3 tablespoons each of sugar, lemon juice, and water; microwave for 1 minute, and cool.