01 -
Combine flour, cold butter, both sugars, salt, and cinnamon in a small bowl. Cut the butter into the flour mixture using a fork or fingers until pea-sized crumbs form. Stir in reserved diced apples and refrigerate until needed.
02 -
Set oven to 425°F (218°C) and position the rack in the middle. Line a muffin pan with four paper liners.
03 -
In a medium bowl, whisk sour cream, pumpkin, apple juice, granulated sugar, brown sugar, egg yolk, and vanilla extract until smooth. Fold in diced apples.
04 -
In a separate bowl, whisk together flour, baking soda, salt, and pumpkin pie spice.
05 -
Sprinkle dry mixture over wet ingredients and gently fold with a spatula until just combined without streaks, avoiding overmixing to prevent toughness.
06 -
Divide batter evenly among the prepared liners and top each with equal portions of chilled streusel topping.
07 -
Bake at 425°F (218°C) for 5 minutes to encourage rising.
08 -
Reduce oven temperature to 350°F (177°C) and bake for an additional 11 to 13 minutes or until a toothpick inserted near the center comes out mostly clean.
09 -
Allow muffins to cool in the pan on a wire rack for 10 minutes before transferring them to the rack to cool completely.