Melt butter and unsweetened chocolate squares in a small saucepan over low heat, stirring constantly; remove from heat.
Beat eggs at medium speed with an electric mixer 2 minutes. Gradually add 1 cup granulated sugar, beating until blended. Gradually add chocolate mixture, flour, vanilla, and salt, beating until blended. Stir in 2/3 cup chopped pecans.
Pour mixture into a lightly greased 9-inch pie plate.
Bake at 350° for 20 to 25 minutes or until center is firm. Serve pie warm with Raspberry Sauce and desired toppings.