How to Make It
Preheat oven to 325°F. Stir together cracker crumbs, 1/4 cup of the granulated sugar, and melted butter in a small bowl. Press mixture into a lightly greased 9-inch fluted tart pan with removable rim, pressing evenly up sides and on bottom.
Bake in preheated oven until crust is lightly browned, 12 to 14 minutes.
Meanwhile, combine cornstarch, salt, and remaining 1 1/4 cups granulated sugar in a medium-size heavy saucepan. Whisk in juices and egg yolks. Using a small wooden pick, stir in a small amount of deep pink food coloring gel. Cook over medium, whisking constantly, until mixture comes to a boil. Boil, whisking constantly, 1 minute. Remove from heat; whisk in 1/3 cup butter pieces.
Pour filling into prepared tart shell. Chill uncovered 4 to 24 hours.
Beat cream with an electric mixer at medium-high speed until foamy; gradually add powdered sugar, beating until soft peaks form. Dollop over tart. Top with quartered grapefruit slices.
For a pretty garnish, cut thin grapefruit half-moon slices; then make one incision from the center to the rind. Gently twist the center until it creates a helix-like shape. The slices will keep their shape once nestled into the whipped cream.