1 lg. can pineapple rings
1 1/2 c. pineapple juice (from can)
1/2 c. sugar
3 tbsp. flour
1/4 c. butter

Place pineapple rings in shallow baking dish. Bring juice and butter to a boil in a saucepan. Mix flour and sugar together and add to boiling juice very slowly. Cook until slightly thick. Pour this over pineapple rings and bake 30 minutes at 350 degrees. If desired, add marshmallows on top and bake until browned.