In a pitcher, muddle the sugar cubes with the club soda until the sugar is fully broken up. Add the remaining ingredients (except the champagne) and fill the pitcher three-quarters full with ice cubes. Stir until cold, then strain into a punch bowl over 1 large block of ice. Top with the champagne. Garnish with the grapefruit wheels and serve with a ladle and punch glasses.
CINNAMON ORANGE TEA–INFUSED SWEET VERMOUTH
In a large container, combine 3 heaping tablespoons of cinnamon-orange tea and one 750-ml bottle of Martini sweet vermouth and stir well. Let stand at room temperature for 1 1/2 hours, stirring occasionally. Strain through a cheesecloth-lined sieve.
Cook note:
You will have plenty of extra tea-infused sweet vermouth, which you can use in place of regular sweet vermouth in a range of cocktails.