Freeze 1 cup butter 10 minutes.
Pulse flour, 1/4 cup superfine sugar, and salt in a food processor 2 or 3 times or until blended. Add butter; pulse 15 times or until mixture is crumbly. With processor running, add 1/4 cup ice water through food chute. Process 10 seconds or just until blended.
Turn dough out onto a sheet of aluminum foil; shape into a 7-inch round. Cover tightly, and chill at least 1 hour or up to 2 days.
Place pumpkin halves, cut side down, in a large, shallow pan.
Bake at 500° for 20 to 25 minutes or until tender. Remove from oven, and cool to touch.
Scoop out pulp, reserving 6 cups.
Melt 1/4 cup butter in a heavy skillet; add 2 cups sugar, and cook over low heat, stirring constantly, until sugar melts and turns a deep-golden color. Carefully stir in pumpkin pulp (mixture will lump but become smooth with further cooking); cook, stirring constantly, until mixture is smooth. Spoon mixture into a bowl; chill 1 hour or until thoroughly chilled.
Roll dough into an 18-by-15-inch oval on a floured surface; carefully transfer to a baking sheet (dough is very tender). Spoon pumpkin mixture over dough, leaving a 2-inch border. Gently lift border, and fold over filling, pleating dough as necessary.
Bake at 450° for 18 to 22 minutes or until crust is golden.
Sprinkle warm tart with powdered sugar. Serve with Caramel Sauce, Nanci Courtney's Cremé Anglaise, and whipped cream.