Step 1

Preheat the oven to 375 degrees F. Butter a 2-quart shallow baking dish or eight 6-ounce ramekins.

Step 2

Make the topping: Whisk the oats, flour, brown sugar and salt in a bowl. Stir in the walnuts. Work in the butter with your fingers until evenly moistened.

Step 3

Make the filling: Peel the apples and cut into 3/4-inch chunks. Toss with the raspberries, granulated sugar, flour, vanilla, nutmeg, cinnamon and salt in a large bowl.

Step 4

Transfer the filling to the prepared dish or ramekins and dot with 2 tablespoons butter. Squeeze handfuls of the crumble mixture and scatter on top of the fruit. Bake until golden and bubbly, 40 to 45 minutes.

Step 5

Let sit 10 minutes before serving. Top with whipped cream or ice cream, if desired.