Beat 1/2 cup margarine and shortening at medium speed of an electric mixer until creamy. Gradually add 2 cups sugar, beating well. Add eggs, one at a time, beating after each addition. Add chocolate and 2 teaspoons vanilla; beat well. Combine flour and 1/4 teaspoon salt; gradually add flour mixture to creamed mixture, mixing well. Stir in peanut butter morsels.
Drop dough by tablespoonfuls onto lightly greased cookie sheets. Bake at 350° for 8 minutes. Cool slightly on cookie sheets; remove from cookie sheets, and let cool completely on wire racks.
Combine evaporated milk and next 5 ingredients in a small saucepan. Cook over medium heat, stirring constantly, 3 to 4 minutes or until thickened and bubbly. Remove from heat; stir in chocolate morsels and 1/2 teaspoon vanilla. Gently stir until chocolate melts. Let cool.
Place about 1 rounded teaspoon chocolate mixture on the bottom of half the cooled cookies; top with remaining cookies.