Preheat your oven broiler.

Slice two of the grapefruits in half. Slice the third into 1/2 inch slices and then again in half. (to create the wedges as shown). Place all the grapefruit on a cookie sheet.

In a small bowl, combine the brown sugar and white sugar. Liberally top the grapefruit halves as well as the slices with the sugar mixture.

Place under the broiler for 8-10 minutes or until the grapefruit is toasted/caramelized.

Remove from the oven, setting aside the sliced grapefruit wedges to use as garnish. Squeeze the grapefruit halves into a cocktail shaker, the juice should equal one cup.

Mix in the lime juice, agave nectar, and tequila. Add in some ice and shake until fully combined.

On a small plate, mix together 2 parts course sea salt to one part dried rosemary. Wet part of each glass and dip in the salt mixture.

Pour the margaritas over ice and garnish with the broiled grapefruit wedges. If topping with the sparkling water splash, do that at the end.

Enjoy!