01 - 
                Combine flour, cold butter, light brown sugar, granulated sugar, salt, and cinnamon in a small bowl. Use a fork or fingers to cut butter into the mixture until pea-sized clumps form. Stir in diced apples. Refrigerate until needed.
              
              
              
                02 - 
                Preheat oven to 425°F (218°C) and position the rack in the middle. Line 4 muffin cups with liners.
              
              
              
                03 - 
                In a medium bowl, whisk together sour cream, pumpkin, apple juice, granulated sugar, brown sugar, egg yolk, and vanilla 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 no dry streaks remain, taking care not to overmix.
              
              
              
                06 - 
                Divide batter evenly among the muffin liners. Top each with equal portions of the chilled streusel topping.
              
              
              
                07 - 
                Bake at 425°F (218°C) for 5 minutes to achieve lift, then reduce heat to 350°F (177°C) and continue baking for 11 to 13 minutes, or until a toothpick comes out mostly clean.
              
              
              
                08 - 
                Allow muffins to cool in the pan on a wire rack for 10 minutes before transferring to the rack to cool completely.