Cream butter in a large mixing bowl; gradually add sugar and vanilla, beating until light and fluffy. Stir in flour, chocolate morsels, and pecans.
Press dough evenly into an ungreased 15-x 10-x 1-inch jellyroll pan. Bake at 350° for 25 to 30 minutes. Cut into 3- x 1-inch bars while warm. Cool completely in pan.