Cut potatoes into 1/8-inchthick slices; place in a bowl of salted water, and soak 1 hour. Drain well.
Place one-fourth of the potatoes in a greased 2-quart casserole; top with one-fourth each of salt and flour. Dot with one-fourth of butter and onion. Repeat layers 3 more times.
Pour whipping cream over final layer. Cover and bake at 350° for 45 minutes; uncover and bake an additional 15 minutes or until lightly browned.