Prepare the Streusel: In a small bowl, combine flour, butter, sugars, cinnamon, and salt. Use your fingers or a fork to mix until crumbly. Stir in diced apple. Refrigerate.
Make the Muffin Batter: Preheat the oven to 425°F. In a bowl, mix sour cream, pumpkin puree, apple juice, both sugars, egg yolk, and vanilla. Stir in diced apples.
In another bowl, whisk together flour, baking soda, salt, and pumpkin pie spice. Fold into the wet ingredients until just combined.
Assemble and Bake: Line a muffin tin with paper liners. Scoop batter into muffin cups. Top with streusel. Bake at 425°F for 5 minutes, then reduce temperature to 350°F and bake for 11-13 minutes or until a toothpick comes out clean.
Let cool for 10 minutes in the pan, then transfer to a wire rack to cool completely.