Heat oven to 350°F. Spray 9-inch square tart pan with removable bottom with cooking spray. Mix crust ingredients. Press lightly into pan. Bake 10 to 12 minutes or until lightly browned. Cool.
In heavy saucepan, mix 1/2 cup sugar, the cornstarch and salt. Stir in juice and yolks with whisk. Cook over medium-high heat 10 to 12 minutes, stirring constantly, until mixture thickens and boils. Remove from heat; stir in 3 tablespoons butter and the grapefruit peel. Pour filling into baked crust. Cover surface of filling directly with plastic wrap. Refrigerate 2 hours 30 minutes.
Place grapefruit sections in large glass bowl; sprinkle with 2 tablespoons sugar. Refrigerate. Before serving, drain grapefruit. Arrange segments on filling.