Preheat oven to 350°F and set a 9x9-inch baking pan aside.
Cut the 1 cup cold butter into small cubes and add to a medium mixing bowl.
Add the 1 cup rolled oats, 1 cup light brown sugar, 1 cup all-purpose flour, 1 tablespoon powdered milk, ½ teaspoon ground cinnamon, and ¼ teaspoon salt to the bowl with the butter and mix until a crumble forms. You can use a pastry cutter, but I prefer to work with my hands, pinching the butter cubes and working them into the ingredients until they all clump together. Do not use an electric mixer.
Peel and chop up the apples into ¾-inch cubes. I usually slice a side off of the apple and cut that into 16 pieces, then use that cut pattern for the rest of the apple. You want around 700 to 800 grams of chopped apples for this recipe.
Add the chopped 5 Honeycrisp apples, ½ cup light brown sugar, ¼ cup all-purpose flour, 1 tablespoon lemon juice, 1 teaspoon vanilla extract, 1 teaspoon ground cinnamon, ¼ teaspoon ground nutmeg, ¼ teaspoon cardamom, and ½ teaspoon salt to a large bowl and stir until evenly coated.
Once the rest of the ingredients have been prepared, rinse 1 pint frozen blueberries under cold water until it runs mostly clear, and then pat them dry between paper towels.
Gently stir the blueberries into the apple mixture and transfer to the 9x9-inch baking dish.
Spread the topping out over the apple mixture.
Bake for 30 minutes until the crisp is browning and the apple mixture is bubbling around the edges.
Loosely tent with aluminum foil and bake for an additional 10 minutes.
Remove from oven and let set. I prefer this recipe to rest for an hour or two before serving; the juices tend to thicken up as they sit.