1/4 teaspoon cream of tartar
6 tablespoons sugarInstructions
In a saucepan, combine 1/ cups sugar and cornstarch. Gradually add grapefruit juice and water, stirring until well blended. Cook and stir over medium-high heat until thickened and bubbly, about two minutes. Reduce heat; cook and stir two minutes longer. In a bowl, lightly beat egg yolks; gradually stir in cup hot mixture and add to saucepan. Bring to a gentle boil; cook and stir for two minutes. Remove from heat; stir in butter and extract. Pour hot filling into prepared shell.
In a mixing bowl, beat reserved egg whites and cream of tartar on medium speed until foamy. Gradually beat in 6 tablespoons sugar, 1 tablespoon at a time, on high speed until stiff peaks form. Spread over hot filling, sealing edges to crust. Bake at 350° until golden brown. Cool for one hour. Refrigerate for three hours before serving. Store in refrigerator.