Melt butter and pour into a 9x13 pan, add 1 box stuffing mix and press into bottom of pan to form crust. Boil squash and mirepoix in water until tender - do not over cook. Mix sour cream, soup, cheese, cooked and drained squash mirepoix mixture and 1 box of stuffing mix in a bowl stir until well blended. Spread squash mixture evenly on top of crust. Bake 350 deg for 30 minutes.