I have my Grandmother's cookbook circa 1940, and the directions say to use cornstarch and put all the ingredients in a pot and cook it until the cornstarch thickens and is semi clear. I usually put the rubbarb and or strawberries in the same pot. I have made her pie without fail, for years. She always made one crust pie and made a simple oat crumble on top, really good with fresh whip cream