Tangy rhubarb crumble with a sweet, buttery oat topping transforms tart rhubarb into a delightful family dessert. This easy, rustic spring classic balances sour and sweet perfectly.
Preheat your oven to 375°F (190°C) and lightly grease an 8x8-inch baking dish.
Gently toss chopped rhubarb with half the sugar and vanilla extract, then spread evenly in the prepared dish.
In a large bowl, combine flour, oats, the remaining sugar, cinnamon, and salt. Mix well to distribute dry ingredients.
Cut cold butter into small cubes and work it into the oat mixture using fingertips or a pastry cutter until the topping forms moist, crumbly clumps.
Evenly sprinkle the crumble topping over the rhubarb, pressing down lightly to ensure some topping sticks together.
Bake on the center rack for 40–45 minutes, until the topping is golden brown and crisp, and the rhubarb filling is bubbling at the edges.
Let cool for at least 15 minutes before serving, allowing the juices to settle for easy scooping.