8 ounces orange liqueur, such as Cointreau or triple sec
1 lime, juiced
4 dashes orange bitters
8 sugar cubes
1 bottle Champagne, chilled
Pour gin, orange liqueur, lime juice, and bitters into a cocktail shaker filled with ice. Shake well to blend. Put a sugar cube into a Champagne flute. Strain about 2 ounces of the gin mixture into the glass. Carefully top it off with Champagne.