- On a work surface, cut 1 round slice of grapefruit from one of the grapefruit halves. Juice the remaining grapefruit to obtain ¼ cup (60 ml) of juice.
- Cut the grapefruit slice into 4 pieces and place on a baking sheet. Sprinkle with sugar. Quickly caramelize using a culinary torch or under the broiler. Let cool.
- In a blender, finely crush the ice with the grapefruit juice and the remaining ingredients until frothy. Pour into two martini or margarita glasses. Garnish with the caramelized grapefruit pieces.
Grapefruit syrup can be found in most grocery stores or made from scratch (see recipe).