Toss together first 4 ingredients.
Melt butter in a large skillet over medium-high heat; add apple mixture, and cook, stirring often, 15 to 20 minutes or until tender. Remove apple and pear with a slotted spoon, reserving juices in skillet. Cook juices over medium-high heat, stirring occasionally, 10 to 15 minutes or until slightly thickened and caramel colored. Remove caramel sauce from heat, and set aside.
Unfold piecrusts, and stack on a lightly floured surface. Roll into a 15-inch circle. Place on a lightly greased parchment paper-lined baking sheet. Arrange apple and pear, cut sides down, in center of pastry, leaving a 3-inch border around edges. Lift pastry edges, and pull over fruit, leaving a 4- to 6-inch circle of fruit showing in center; press folds gently to secure. Stir together egg and 1 tablespoon water; brush over pastry. Sprinkle with 2 tablespoons sugar.
Place the lightly greased sides of a 9-inch springform pan with clasp open around pie; close clasp.
Bake on lowest oven rack at 425° for 30 to 35 minutes or until golden brown. Run a knife around edges of pie to loosen. Cool on baking sheet on a wire rack 10 minutes. Remove pan sides.
Heat caramel sauce over medium heat.
Beat whipping cream at medium speed with an electric mixer until foamy; gradually add remaining 3 tablespoons sugar and, if desired, liqueur, beating until soft peaks form. Serve sauce and whipped cream with pie.
Note: Do not substitute wax paper or aluminum foil in this recipe. Parchment paper is packaged similarly to wax paper.
* Gala or Rome apples may be sustituted for Granny Smith.
** Bosc or Anjou pears may be substituted for Bartlett.