Pour the Cognac, simple syrup, and lemon juice into a cocktail shaker and add the ice. Shake for at least 30 seconds (it’s longer than you think!). Pour the mixture into 4 Champagne flutes to fill each glass about two-thirds full. Fill the glasses with Champagne, garnish with the lemon zest, and serve ice cold.
For this simple syrup, combine 1 cup water and 1 cup sugar in a small saucepan, bring to a boil, and cook until the sugar dissolves. Cool.
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