Cut each grapefruit in half crosswise.
Remove any pits and cut around each section with a sharp knife.
Sprinkle each grapefruit with 1 teaspoon sugar.
Dot each half with 1/2 teaspoon of butter.
Place grapefruit halves on a paper plate.
Heat, uncovered, on full power 4 minutes.
Garnish each half with a maraschino cherry.