Rhubarb Breakfast Crisp

From the garden

• 5 cups rhubarb stalks, trimmed and sliced ½ inch thick (about 1½ pounds)
• 1 cup rolled oats · old-fashioned, not instant

From the pantry

• ⅔ cup granulated sugar · for the fruit
• 2 tbsp cornstarch
• ¾ cup all-purpose flour
• ½ cup brown sugar · for the topping
• 6 tbsp butter, melted · plus more for the dish
• ¼ tsp salt
• plain Greek yogurt · to serve

1. Heat the oven to 375°F and butter an 8-inch baking dish. Toss the sliced rhubarb with the granulated sugar and cornstarch until evenly coated, then tip into the dish: it looks like a lot, but it slumps as it bakes.
2. Stir the oats, flour, brown sugar, and salt together, then pour in the melted butter and mix until the crumble clumps when squeezed.
3. Scatter the topping over the rhubarb in uneven clusters: the craggy bits are what get crunchy.
4. Bake 35–40 minutes, until the topping is deep golden and pink juices bubble thickly at the edges. If the crumble browns before the fruit bubbles, it isn't done: the bubbling is the cornstarch thickening.
5. Rest at least 15 minutes so the juices set from soupy to jammy, then spoon into bowls over thick yogurt, warm or at room temperature.