When grapefruits are in season, try using them in place of store-bought margarita mix for a refreshing twist on a classic cocktail. To make frozen margaritas, add ice to the mixture and whirl in a blender until smooth.
Combine the sugar and water in a small pan and set over high heat. Cook until the sugar dissolves, stirring occasionally. Let the mixture boil for one minute and then remove the pan from the heat. Cool and then chill the syrup until it is cold.
Combine 1/4 cup of the sugar syrup, grapefruit juice, Triple Sec, and tequila in a pitcher and stir to blend. Keep refrigerated until ready to serve. Serve over crushed ice, if you like.