Preheat the oven to 375°F.

Toss the apples and blackberries in a large bowl with the lemon juice, vanilla extract, and granulated sugar.

Sprinkle 2 tablespoons of flour and ground cinnamon over the fruit, then toss to combine.

Set the bowl aside while preparing the topping. This will allow the fruit time to begin to extract some juices.

Mix the rolled oats, ½ cup of flour, and the brown sugar in a separate medium bowl.

Cut the butter into chunks and add it to the flour mixture. Work the butter into the mixture using a wooden spoon or your hands until the mixture turns crumbly.

Pour the fruit, along with the juices, into a deep dish pie plate or 1 1/2-quart baking dish.

Sprinkle the topping evenly over the fruit. The topping will be higher than the sides of the baking dish, but will shrink down as the filling cooks.

Bake in the oven for 35-45 minutes, or until the crumble topping is golden brown and the filling is bubbly.

Remove from the oven and let cool for 10-15 minutes.

Serve with ice cream or whipped cream.