Grapefruit is back! Grilling caramelizes the sugars and adds smoky depth—a slice makes a delicious garnish for a brunch cocktail, and leftovers are good cold.
In a bowl, combine sugar and cinnamon or cayenne, if using. Cut grapefruit in half around their equators.
Place grapefruit, cut-side down, on a preheated medium grill. Close lid and cook until edges are charred and the surface is grill-marked, about 5 minutes.
Turn over. Sprinkle cut sides generously with sugar mixture. Close lid and continue cooking until sugar is caramelized and grapefruit are softened, about 5 minutes more.
Tip: To serve, cut inside the rind to loosen the flesh, then cut grilled grapefruit into quarters.