1. 1. Prepare your baking dish and oven: Preheat your oven to 375 F (190 C). Lightly grease a 9×13 inch baking pan with butter or cooking spray. This helps prevent sticking and makes serving easier.

2. 2. Combine the rhubarb filling: In a large bowl, combine the chopped rhubarb, 1 cup of granulated sugar, and ¼ cup of all-purpose flour. Toss gently until the rhubarb is evenly coated. Pour the rhubarb mixture evenly into the prepared 9×13 inch baking pan.

3. 3. Mix the dry crumble topping ingredients: In a separate medium bowl, whisk together the remaining ½ cup granulated sugar, 1 ½ cups all-purpose flour, packed light brown sugar, ground cinnamon, and salt. Make sure there are no lumps in the brown sugar.

4. 4. Incorporate the butter into the topping: Add the cold, cubed butter to the dry topping ingredients. Using your fingertips, a pastry blender, or a fork, cut the butter into the flour mixture until it resembles coarse crumbs with some pea-sized pieces remaining. Avoid overmixing; you want distinct pieces of butter to create that signature crumble texture.

5. 5. Assemble the crumble: Evenly sprinkle the crumble topping over the rhubarb mixture in the baking pan. Ensure the rhubarb is mostly covered, creating a beautiful golden crust as it bakes.

6. 6. Bake until golden and bubbly: Place the baking pan in the preheated oven and bake for 45-55 minutes, or until the topping is golden brown and the rhubarb filling is bubbly around the edges. The bubbling indicates that the rhubarb is tender and the juices have thickened.

7. 7. Cool before serving: Remove the crumble from the oven and let it cool on a wire rack for at least 15-20 minutes before serving. This allows the filling to set slightly, making it easier to scoop and preventing it from being too runny.