*Shredded Preheat oven to 325F (163 °C). Melt butter or margarine over low heat. Pour the popcorn into a large 4-inch deep baking pan. Add butter, garlic salt, onion salt, and cheese, a small amount of each at a time, and toss. Heat in the oven for 5 to 10 minutes to melt the cheese, stirring gently once or twice. Yield: Makes 4 quarts.

which says they got the recipe originally from Hunt-Wesson Foods.