Edna's cookies

David and I have been making cookies, the last batch being chocolate chip.  We've been having trouble with this recipe.  They have been hard little rocks.  We went backto our old margarine, and beat the margarine and sugar more than we had been.  I even remembered to add the vanilla, which I haven't done in years.  But no melt in your mouth cookies--more like pave the walk cookies.  I have a vague memory of Mom saying that the extra 1/3 cup of flour was optional to adjust for the temperature in the house.  Makes sense to me as the margarine would be softer in a hotter house.  What  have been your experiences?  I would hate to think that my new mixer is the problem.