Add your fruit mixture ingredients (fruit, sugar, flour, sand a pinch of salt) directly to the baking dish and stir them to combine. Adjust them until they make an even layer.
2 cups fresh blueberries, 4-5 apples, 1/4 cup sugar, 1/4 cup flour, 1 pinch kosher salt
In a small bowl, combine crumble topping ingredients. Using a pastry blender, mix the butter pieces into the crumble topping until the mixture looks like crumbly sand.
1 1/2 cup rolled oats, 1/2 cup flour, 1 cup brown sugar, 1/4 cup white sugar, 1 tsp vanilla extract, 1 pinch kosher salt, 2 sticks unsalted butter
Add the crumble mixture on top of the fruit mixture and bake for 45-50 minutes or until the topping is golden brown and the fruit is bubbling in the corners of the pan.
Remove from the oven and let the apple blueberry crumble rest for 25-30 minutes before serving with a scoop of ice cream or a dollop of whipped cream.
Notes
Store leftover crumble in an airtight container in the fridge for 4-5 days. I often just keep the crumble in my baking dish and cover it with a piece of beeswax wrap or another plastic wrap alternative.To reheat, microwave a serving for approximately 1-2 minutes or bake it at 350 degrees for 4-5 minutes or until fully heated.
Work with cold butter. If your butter isn't really cold, it will melt into the blueberry apple mixture instead of turning into a delicious crumble topping.
Get chilly. I actually like to chill my crumble topping before adding it to the pan. This isn't necessary, but it gives me the most perfect, sky-high crumble!
Add spices & seasonings. You can easily tweak this fruit crumble recipe by adding your favorite spices (cinnamon, allspice, Chinese 5 Spice) or adding aromatic ingredients like lemon juice, lemon zest, lavender extract, etc.
Add nuts. For extra crunch and flavor, replace 1/4 cup of the oats with chopped almonds or pecans.