01 -
Combine oats, flour, brown sugar, and melted butter. Reserve 1/3 of the mixture for the topping and press the rest into a greased baking dish.
02 -
Cook rhubarb, sugar, and cornstarch in a saucepan over medium heat until thickened. Let it cool slightly before spreading over the base.
03 -
Sprinkle the reserved oat mixture over the rhubarb filling. Bake at 350°F for 35–40 minutes or until golden brown.