- 3 cups diced rhubarb
- 1 1/4 cups white sugar
- 2 tablespoons all-purpose flour
- 1 large egg
- 1/2 teaspoon ground cinnamon
- 1 1/2 cups all-purpose flour
- 1 cup packed light brown sugar
- 1 cup quick-cooking oats
- 1/2 teaspoon ground cinnamon
- 1 cup butter
- Preheat oven to 375 degrees F (190 degrees C). Lightly grease a 9×13-inch baking dish.
- Combine rhubarb, white sugar, 2 tablespoons flour, egg, and 1/2 teaspoon cinnamon together in a large bowl until evenly coated. Spread rhubarb mixture into the prepared baking dish.
- Mix 1 1/2 cup flour, brown sugar, oats, and 1/2 teaspoon cinnamon together in a separate bowl. Cut in butter using a pastry cutter or two forks until topping is crumbly. Sprinkle topping over rhubarb layer.
- Bake in the preheated oven until hot and bubbling, about 40 minutes. Serve hot or cold.