1 1/2 cups all-purpose flour 1 cup rolled oats 1 cup packed brown sugar 1 teaspoon ground cinnamon 1 cup (2 sticks) cold unsalted butter, cut into pieces 1 1/2 cups chocolate chips or chopped nuts (optional)
Preheat oven to 350°F. Line a baking sheet with parchment paper and set aside.
In a large bowl, whisk together the flour, oats, brown sugar, and cinnamon until well combined.
Cut in the butter using a pastry blender or your fingers until mixture resembles coarse crumbs. Stir in chocolate chips or nuts if using.
Crumble mixture evenly onto the prepared baking sheet. Bake for 18-20 minutes, stirring halfway, until golden brown.
Allow crumble to cool completely on baking sheet. Break into pieces and serve over ice cream or enjoy on its own for a sweet and crunchy treat!