Cream butter in a large mixing bowl; gradually add sugar, beating well. Add eggs, one at a time, beating well after each addition. Add melted chocolate, and beat until blended. Gradually add flour, stirring well. Stir in vanilla and pecans. Pour batter into a greased 8-inch square baking pan.
Bake at 350° for 25 minutes. Cool brownies completely in pan. Cut into 2-inch squares.