In a small mixing bowl, add the flour, butter, both sugars, salt, and cinnamon. Cut the butter into the flour until you have small pea size pieces of streusel. Stir in the reserved diced apples. Refrigerate the streusel topping until ready to use.

Preheat oven to 425°F and adjust oven rack to the middle position. Line the muffin pan with 4 muffin liners.

In a medium mixing bowl, add the sour cream, pumpkin, juice, both sugars, egg yolk, and vanilla extract. Mix until combined and smooth. Stir in the remaining apple cubes.

In a small mixing bowl, whisk together the flour, baking soda, salt, and pumpkin pie spice. Sprinkle the dry ingredients over the wet ingredients. Fold until no dry streaks remain, being careful not to overmix.

Evenly scoop the batter into the prepared muffin liners. Top each muffin with equal portions of the streusel topping.

Bake at 425°F for 5 minutes, then reduce the heat to 350°F and bake for an additional 11 to 13 minutes, or until a toothpick inserted in the middle comes out mostly clean.

Cool the muffins in the pan set on a wire cooling rack for 10 minutes, then transfer to the wire rack to cool completely.