In a medium bowl, combine ⅓ cup white flour, 1 tablespoon quick cooking oats, ½ teaspoon cinnamon, and 2 tablespoons brown sugar. Cut in 2 tablespoons of cold stick butter until the mixture resembles coarse crumbs. Chill this streusel topping in the refrigerator while you prepare the muffin batter.

Preheat your oven to 425°F (220°C). Line a muffin tin with paper liners.

In a large mixing bowl, whisk together ½ cup white flour, ¾ cup whole wheat flour, 2 tablespoons cornstarch, 1 teaspoon baking powder, ¼ teaspoon salt, 1 teaspoon cinnamon, and ½ teaspoon apple pie spice.

In a separate bowl, whisk together 1 large egg, ¾ cup plain Greek yogurt, ¼ cup oil, 2 tablespoons maple syrup, 1 teaspoon vanilla extract, and ⅓ cup light brown sugar.

Gently fold the wet ingredients into the dry ingredients, mixing just until combined. Fold in 1 cup of peeled and chopped apple.

Scoop the batter into the prepared muffin cups, filling each about three-quarters full. Sprinkle the chilled streusel topping over each muffin.

Bake at 400°F (200°C) for 5 minutes, then lower the temperature to 350°F (175°C) and continue baking for 15 to 18 minutes.

Allow the muffins to cool in the tin for about 5 minutes, then transfer them to a wire rack to cool completely.