Beat 1 cup softened butter in a large mixing bowl at medium speed with an electric mixer until creamy.
Stir together 2 cups flour, 1/2 cup granulated sugar, and salt. Add to butter mixture, beating until crumbly. Stir in pecans.
Press dough into an ungreased 13- x 9-inch pan.
Bake at 350° for 25 minutes or until golden.
Microwave chocolate morsels and 3/4 cup butter in a 2-quart glass bowl at HIGH 1 1/2 minutes or until melted, stirring twice.
Whisk in eggs, vanilla, remaining 1 cup granulated sugar, and remaining 1/2 cup flour until smooth. Pour chocolate mixture over prepared crust.
Bake at 350° for 25 minutes or until set. (Do not overbake.) Cool completely in pan on a wire rack. Cut into 24 bars. Transfer bars to wax paper; dust with powdered sugar. Store bars in an airtight container. If desired, serve with whipped cream or ice cream, and sprinkle with chocolate shavings.