Whisk flour and salt in a bowl.

Using pastry blender, or in food processor with pulsing action, cut shortening into flour mixture until consistency of peas. Cut in butter. Add 3 to 4 tablespoons cold water, a little at a time. Toss with a fork or pulse in food processor until dough holds together.

Gather dough and transfer to a sheet of plastic wrap; gently flatten into a disk. Wrap and refrigerate at least 2 hours.

Heat oven to 425 degrees F. On floured surface, roll dough into a 12-inch circle. Roll up onto rolling pin and transfer to a 12-inch pizza pan. Fold over edge to form a slight lip. Bake at 425 degrees F for 8 to 10 minutes. Remove from oven.

Topping: Cut peel and white pith from grapefruit. Slice fruit in thin slices; cut slices in half. Dry on paper towels.

Spread marmalade on baked crust. Top with cookie crumbs. Fan grapefruit slices over crust; sprinkle with 3 tablespoons of the sugar. Bake at 425 degrees F for 20 to 22 minutes, until crust is browned. Remove tart from oven; turn on broiler. Sprinkle tart with remaining 3 tablespoons sugar. Run under broiler for 2 to 3 minutes, until shiny and browned.