Slice the grapefruits in half and line on a cookie sheet.
Sprinkle each grapefruit top with a spoonful of granulated sugar making sure to cover the entire top of the grapefruit.
Use kitchen blowtorch or broiler to heat sugar. For the broiler, leave the grapefruits in the oven for 5-7 minutes. If using a blowtorch, it takes about 1-2 minutes to heat the sugar per grapefruit.
Notes
Grapefruit brulee does not store well. Eat right away.