Preheat oven at 500 degrees.
Cut the grapefruit in halves crosswise. Cut off the sections, and discard the membranes from grapefruit. Chill shells upside down on a baking tray.
In a mixing bowl, combine the grapefruit sections with the grenadine. Chill for 30 minutes Strain grapefruit sections and save 2 tablespoons of the grenadine juice.
In an electric mixer, combine the egg whites with the cream of tartar. Beat the egg whites until light and fluffy, then stir in the grenadine juice and sugar.
Continue beating until meringue is thick and firm.
Scoop the raspberry sorbet into the grapefruit shells, filling the shells half way.
Arrange the grapefruit sections on top of sorbet.
Spread meringue over the grapefruit, sealing well at edges of shells.
Bake for about a minute in oven, or until golden brown