This version of rhubarb crumble uses oats in the crumble mixture, and also is rather unusual in putting some crumble mixture as a layer on the bottom (not just on top).
1 cup brown sugar
¾ cup oats
1 cup flour
½ cup butter
1 tsp cinnamon
4 cup uncooked diced rhubarb
1 cup white sugar
2 tbsp corn starch
1 cup water
1 tsp vanilla
Mix brown sugar, oats, flour, butter, and cinnamon until crumbly.
Press half the mixture into a 9 inch square pan.
Cover crumb mixture with diced rhubarb.
Mix white sugar, cornstarch, and water. Cook until clear and thick, stirring constantly. Add vanilla and stir.
Pour over rhubarb. Sprinkle with remaining crumb mixture over the top.
Bake for 1 hour at 180°C.
1 hour