In a large bowl, cream butter and sugars. Add the eggs, one at a time, beating well after each addition. Stir in molasses and vanilla; mix well. Combine dry ingredients; gradually add to creamed mixture. , Drop by tablespoonfuls 2 in. apart onto ungreased baking sheets. Bake at 325° for 12-15 minutes or until cookies spring back when touched lightly (do not overbake). Remove to wire racks. , For frosting, in a large saucepan, bring the brown sugar, milk and butter to a boil; cook and stir for 1 minute. Remove from the heat (mixture will look curdled at first). Cool for 3 minutes. Add confectioners' sugar, vanilla and salt; mix well. Frost warm cookies.