• Preheat the oven to 425F degrees and adjust the oven rack to the middle position. Line the muffin pan with 4 muffin liners. Tulip liners are ideal for keeping the streusel contained on top of the muffins. See below for how to make your own.
• Dice the apple into about 1/4 inch cubes for the muffins. From that, take out about 1 ½ tablespoons and chop those pieces even smaller (about half the size) for the streusel topping.
  

Apple Streusel Topping

• In a small mixing bowl, add the flour, butter, both sugars, cinnamon, and salt. Cut the butter into the flour using a fork or your fingers, and mix until you have pea-sized, moistened crumbs.
  3 tablespoons all-purpose flour, 1 ½ tablespoons unsalted butter, cold and cut into cubes, 1 ½ tablespoons light brown sugar, 2 teaspoons granulated sugar, 1/4 teaspoon ground cinnamon, 1 pinch salt
• Stir in the small apple pieces, then refrigerate the streusel until ready to use.
  1 ½ tablespoons small apple pieces

Apple Pumpkin Muffins

• In a medium mixing bowl, add the pumpkin, sour cream, both sugars, egg yolk, juice, and vanilla. Whisk until combined and smooth.
  1 ½ tablespoons full fat sour cream, room temperature, 5 tablespoons pure canned pumpkin, 1 tablespoon apple juice, 3 tablespoons granulated sugar, 2 tablespoons light brown sugar, 1 large egg yolk, room temperature, 1/2 teaspoon vanilla extract, 1/2 cup fresh apple, cut into small cubes
• Sprinkle the flour, pumpkin pie spice, baking soda, and salt over the wet ingredients. Whisk until no flour streaks or pockets remain. Use a spatula to fold in the remaining apple cubes. Careful not to overmix the batter, or the muffins can be tough and chewy.
  1/2 cup, plus 1 tablespoon all-purpose flour, 1/4 teaspoon baking soda, 1 teaspoon pumpkin pie spice, 1/8 teaspoon salt
If your flour or pumpkin pie spice is clumpy, use a fine-mesh strainer to sift it over the wet ingredients so it distributes and bakes evenly.
• Evenly scoop the batter into the prepared muffin liners. I like to use a cookie scoop for this to get even portions. The muffin liners will be nearly full. Top each muffin with equal portions of the streusel topping. It will seem like a lot, but as the muffins bake, it will spread to cover the muffin tops.
• Bake the muffins at 425F degrees for 5 minutes. The quick time at high heat makes the muffin tops puff up. Then, with the muffins still in the oven, reduce the heat to 350F degrees and bake for an additional 13 to 14 minutes, or until a toothpick inserted in the middle comes out mostly clean. Do not overbake, or the muffins will be dry.
• Cool the muffins in the pan, set on a wire cooling rack for 10 minutes, then transfer to the rack to cool completely. If some of the streusel fell off during baking, press it back onto the top of the warm muffins.
• Store the muffins in a covered container at room temperature for up to 3 days. Beyond that, and they will start to dry out.