A departure from the classic mimosa. You can leave out the simple syrup if want a tarter cocktail.
Make your simple syrup by combining equal volumes of water and granulated sugar in a sauce pot over medium heat, swirling until all of the sugar has dissolved. Cool and store in refrigerator.
In a champagne flute, combine simple syrup with orange liquor. Add freshly squeezed grapefruit juice. Finally top with chilled Prosecco.