A brown sugar crumble tops a fresh, spring-like apple rhubarb filling makes for a sweet and tart dessert. Good after a big meal or as a during-the-week dessert. A refreshing change from chocolate, nuts, and sponge cakes. Substitute cranberries for the rhubarb if you like for a rosy and tart filling, substitute apricots (fresh or canned) for a sweeter filling. Almost any combination of fruits will work.