I agree completely, it's probably the overheating of the cheese that's causing your sauce to break. As everybody said before, add it last or make a roux-based sauce (the starches should trap the oil exuded by breaking cheese fine, keeping the sauce smooth even with vigorous heating).
__________________ "If it's chicken, chicken a la king. If it's fish, fish a la king. If it's turkey, fish a la king." -Bender |