Juice the limes until you have one cup of fresh key lime juice.

If you don’t have simple syrup ready, combine equal parts sugar and water in a small saucepan. Heat gently until the sugar dissolves, then let it cool.

In a mixing pitcher, combine the fresh key lime juice with the simple syrup. Stir well to blend the flavors together.

Ensure your champagne is well-chilled.

Pour about 1/4 cup of the key lime juice mixture into each champagne flute.

Slowly top off each glass with chilled champagne.

If using, add a splash of club soda to each glass for extra fizz.

Garnish each mimosa with a key lime wedge on the rim of the glass. Serve immediately.