With the rack in the middle position, preheat the oven to 350°F (180°C). Line a baking sheet with parchment paper.
In a bowl, combine all of the ingredients with your fingertips until everything is moistened with the butter. Spread out on the baking sheet. Bake for 10 to 12 minutes or until the crumble is golden, stirring a few times. Let cool completely.
Serve the crumble on its own or with milk, yogurt or fruit compote.
The crumble will keep in an airtight container at room temperature for up to 2 weeks.