Prepare the Streusel Topping by mixing the flour, butter, sugars, salt, and cinnamon in a bowl. Cut the butter until pea-sized pieces form. Add reserved diced apples and refrigerate until needed.
Preheat your oven to 425°F and line a muffin pan with 4 liners.
In a medium bowl, combine sour cream, pumpkin, apple juice, both sugars, egg yolk, and vanilla. Mix until smooth and fold in remaining apple cubes.
In a small bowl, whisk flour, baking soda, salt, and pumpkin pie spice. Sprinkle over wet ingredients and fold until combined.
Scoop batter into muffin liners, filling each about ¾ full. Top with streusel topping.
Bake at 425°F for 5 minutes, then reduce to 350°F and bake for 11-13 minutes until a toothpick comes out mostly clean.
Cool muffins in the pan for 10 minutes, then transfer to a wire rack to cool completely.
Notes
For added flavor, consider adding a handful of chopped nuts to the streusel topping.
Keyword Apple Pumpkin Muffins with Streusel Topping Recipe