For the Blackberry Apple Filling
2 ½ cups frozen (or fresh) blackberries
2 ½ cups apples, peeled and thinly sliced (approx. 2 large apples)
Juice of ½ lemon (½ oz)
⅓ cup packed light brown sugar
3 tablespoons all-purpose flour
½ teaspoon ground cinnamon
¼ teaspoon ground nutmeg
Pinch of salt
For the Crumble
1 cup old-fashioned oats
½ cup loosely packed light brown sugar
2 tablespoons all-purpose flour
½ teaspoon cinnamon
¼ teaspoon salt
4 tablespoons unsalted butter, softened
Preheat the oven to 375˚F.
Add all fruit filling ingredients to a large bowl. Stir to combine. Set aside for 5 minutes to let the juices release while you make the crumble.
In a medium mixing bowl, stir together oats, sugar, flour, cinnamon, and salt for the crumble. Add butter and use your hands to mix it in, pinching the butter between your fingers to incorporate it. Mix until combined and the mixture is crumbly (it should feel like wet sand).
Add the fruit mixture to a 10-inch casserole dish or cast iron skillet. Sprinkle the crumble on top in an even layer.
Bake for 35 to 40 minutes, until the filling is bubbly and the top is golden brown.
Let the crumble rest for 5 minutes before serving.
Serve with ice cream, whipped cream, or on its own.
Note: When using frozen blackberries, thaw them first and drain them well before adding them to the fruit mixture.