Mix all ingredients in a cocktail shaker with ice. Pour, unstrained, into a tall glass. Serve it with a straw. Garnish with a sprig of fresh mint.
If you're having a party and want to make a full recipe in a punchbowl, use the entire bottle of wine, a couple generous pours of the sherry and Grand Marnier, and add the sugar to taste. You can also extend the volume and give the punch a little bit of a kick by adding a liter of club soda. Slice up a full lemon and orange, and leave the wedges in the punch bowl.