Juice the fresh grapefruit. One large grapefruit usually yields about ¾ cup. Buy an extra fruit in case you're short, want some slices for garnish, or another round!
Make the cocktail:
Place the grapefruit juice, lime juice, tequila, Cointreau or triple sec, simple syrup, and ice in a blender. Blend on high until smooth. Add more ice if needed.
Serve:
Pour the frozen paloma into two glasses. Garnish with a slice of lime or grapefruit.