Preheat oven to 350°F. In bowl, mix filling ingredients; turn into a 1-quart (4 cups) capacity pie dish.
Rub butter into flour just until mixture resembles coarse breadcrumbs, then stir in sugar.
Sprinkle this mixture over rhubarb in the pie dish. Bake for 30 to 45 minutes until topping is cooked and golden.
Serve with whipped cream and soft brown sugar, or try stirring a little Amaretto into your cream.