You can serve this festive cocktail for New Year's Eve or at brunch on New Year's Day. It's a nice take on a classic, and tequila is very popular right now.
Technique tip: I like to juice my own grapefruit juice and always have simple syrup in the fridge.
Swap option: You can substitute any sparkling wine, such as Prosecco, for the Champagne and cognac for the tequila.
In a coupe or Champagne flute combine the tequila, simple syrup, grapefruit juice, and bitters. Top off with Champagne.