Easy Oat Crumble Topping

Place rack in middle of oven; preheat oven to 375°F.

Whisk 1 cup (125 g) all-purpose flour, ½ cup (107 g) light brown sugar, ½ tsp. baking powder, ½ tsp. ground cinnamon, and ¼ tsp. kosher salt in a large bowl. Add ½ cup (1 stick) unsalted butter at room temperature, cut into pieces, and work into flour mixture with your fingertips until pea-size lumps form. Add ¾ cup (67 g) old-fashioned oats and mix with your fingertips until clumps form; it should look like crumb topping. Chill 15 minutes.

Transfer oat mixture to a parchment-lined rimmed baking sheet; bake 8 minutes. Using a metal spatula, stir and toss crumble. Rotate pan and continue baking until crumble is dark golden brown, about 8 minutes more. Let cool. Do Ahead: Crumble can be prepared 3 days in advance. Let cool completely, then store in an airtight container at room temperature.