PREHEAT oven to 350° F. Grease two 8- or 9-inch round cake pans.
BEAT cake mix, 1 1/2 cups pumpkin pie mix, eggs and oil in large mixer bowl for 2 minutes. Spoon into prepared pans.
BAKE for 25 to 30 minutes or until wooden pick inserted in center of cakes comes out clean. Cool in pans on wire racks for 10 minutes; remove to wire racks to cool completely.
MEANWHILE, WHISK together evaporated milk and cornstarch in medium, heavy-duty saucepan. Stir in remaining pumpkin pie mix and 1 tablespoon liqueur. Heat to boiling over medium heat, stirring constantly. Boil for 1 minute or until thickened; remove from heat. Cover; cool to room temperature.
SPRINKLE remaining 2 tablespoons orange liqueur over tops of cakes. Cut layers in half horizontally. Spread about 3/4 cup filling between layers. Spread top of cake with whipped topping and garnish with orange curls, if desired. Store in refrigerator.