Rhubarb Crumble Pie
["2/3 c. brown sugar", "1 1/2 c. rolled oats", "1/2 c. all-purpose flour", "1/2 c. melted butter"]
["Mix all ingredients and pat mixture into a 9-inch pie plate, reserving enough for topping."]
["brown sugar", "rolled oats", "all-purpose", "butter"]