To broil grapefruit:

1. Turn your oven on broil. Mix brown and white sugars. Place grapefruit slice on a foil-lined cookie sheet. Generously coat the slice of grapefruit with your sugar mixture. Place in the oven for about 8 minutes or until the sugars have caramelized. Remove from the oven and let sit.

For the Margaritas:

1. Fill a shaker with ice.
2. Muddle the rosemary and agave.
3. Add muddled mixture to the shaker.
4. Add grapefruit juice, tequila, and lime juice and shake until the outside is frosted.
5. Pour into an ice-filled glass.
6. Garnish with broiled grapefruit slice and a sprig of rosemary.