Line a 13-in. x 9-in. baking pan with foil; grease the foil with 1 teaspoon butter. In a large bowl, combine the flour, confectioners' sugar and salt. Add vanilla and remaining butter; cut in butter until mixture resembles fine crumbs. Pat into prepared pan.
Bake at 325° for 20-25 minutes or until edges are lightly browned. Cool on a wire rack.
In a large saucepan, combine the chocolate, milk and butter. Cook and stir over low heat until smooth; set aside.
In a large bowl, beat eggs and sugar until thick and lemon-colored. Beat in extract and chocolate mixture. Pour over crust. Bake for 30-35 minutes or until center is almost set. Cool completely in pan on a wire rack.
Refrigerate overnight. Using foil, lift bars out of pan; cut into triangles. Store in the refrigerator.