For crust, stir together flour and powdered sugar. Cut in the 3/4 cup butter until pieces are the size of small peas. Stir in the 1 1/2 cups pecans. Press into a lightly greased 13x9x2-inch baking pan. Bake in a 325 degree F oven 25 minutes or until light brown.
For filling, in a medium saucepan combine light and dark corn syrups, brown sugar, and the 1/4 cup butter. Bring to boiling over medium heat, stirring constantly. Remove from heat. Beat eggs with an electric mixer on low speed until mixed. Continue beating, slowly adding hot mixture. Stir in 2 cups pecans, peel, and vanilla.
Pour filling onto crust. Sprinkle with chocolate pieces. Bake in a 350 degree F oven for 35 to 40 minutes or until center is set. Cool on a wire rack; chill to store. To serve, cut into squares. If desired, serve with Orange Cream and additional finely shredded orange peel.
Orange Cream: Combine 1 cup whipping cream, 2 tablespoons sugar, and 2 tablespoons dairy sour cream; beat until mixture starts to thicken. Add 1 tablespoon orange liqueur or 1/2 teaspoon orange extract, 1/2 teaspoon finely shredded orange peel, and 1/2 teaspoon vanilla; beat on low speed just until soft peaks form (tips curl).