I love to layer this filling in between vanilla cake, then frost with seven-minute icing.  Yum!!

1 can (20 ounces) unsweetened crushed pineapple with juice
3/4 cup sugar
5 tablespoons flour
1/3 cup unsalted butter

To make the filling, in a medium saucepan, combine the pineapple, sugar, flour, and butter. Cook over medium heat, stirring constantly, until thickened. Remove from the heat and cool completely.