Put diced apples and blackberries in a bowl. Add granulated sugar, light brown sugar, all-purpose flour, cinnamon, and nutmeg. Stir to coat.
Spread the coated fruit in a greased 9x13-inch baking dish.
To make the streusel topping, mix the all purpose flour, granulated sugar, light brown sugar, and ground cinnamon together in a bowl. Cut in butter until crumbly.
Spread the streusel topping over the fruit mixture in the baking dish.
Bake at 375˚F for 40-45 minutes, until the apples are tender and the streusel topping is golden brown.
Fridge: Allow it to cool completely, cover the dish, and store it in the fridge for up to four days.
Freezer: After completely cooling the apple and blackberry crumble, wrap it tightly in plastic wrap and then in aluminum foil. Store it in the freezer for up to 3 months. Allow it to thaw in the fridge.
Reheating: You can reheat it in the oven at 350˚F for 10-15 minutes or in the microwave on high for 1-2 minutes, depending on your microwave.
Two: With Oats
Follow the recipe as directed but substitute the flour called for in the streusel with 1 cup of oats and 1 cup of flour.
Three: Blackberry and Pear
Substitute the diced apples with an equal amount of diced pears.