Instead of using fat, such as butter or margarine, I use non stick cooking spray. Take 2 pieces of wheat bread and spray both sides with a non stick cooking spray. Place them in a skillet. When those sides are brown, flip one over, place a piece of low fat cheese on it, then flip the other bread on it, browned side against cheese.
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To make a lower calorie count of a grilled cheese sandwich, spray the outside of the bread with butter flavors or plain Pam spray instead of using butter or margarine. The sandwich will toast beautifully and you have saved all the fat! Delicious!