Instructions

1. 1

   Preheat the oven to 375°F and lightly grease an 8x8-inch baking dish. Toss the chopped rhubarb with granulated sugar, cornstarch, vanilla, and lemon juice until the fruit looks glossy and evenly coated.

2. 2

   Spread the rhubarb mixture into the baking dish in an even layer. The filling may look dry at first, but the rhubarb releases plenty of juice as it bakes.

3. 3

   In a separate bowl, combine the oats, flour, brown sugar, cinnamon, and salt. Add the cold butter cubes and work them into the mixture with your fingertips or a pastry cutter until large crumbs form. The texture should look sandy with some pea-sized butter pieces still visible.

4. 4

   Sprinkle the oat crumble topping evenly over the fruit. Avoid pressing it down too firmly so the topping stays crisp instead of dense.

5. 5

   Bake for 40 to 45 minutes, until the fruit is bubbling around the edges and the topping is deep golden brown. If the crumble starts browning too quickly, loosely tent the dish with foil for the last 10 minutes.

6. 6

   Let the rhubarb crumble cool for at least 15 minutes before serving. The filling thickens as it rests, making it easier to scoop.