Make streusel topping:
In a small bowl, mix flour, brown sugar, cinnamon, and salt. Incorporate the cold butter cubes using a pastry blender until the mixture forms coarse, moist crumbs, roughly 2-3 minutes. Reserve in the fridge until needed.Whisk dry ingredients:
In a medium bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and ginger.Cream butter and sugar:
In a large bowl, cream the softened butter and granulated sugar until pale and fluffy. Add eggs and vanilla, beating thoroughly for about 2-3 minutes.Combine batter and fold apples:
Gradually add the dry mixture and sour cream to the butter mixture in alternating portions, mixing until the batter is thick and slightly aerated, about 3-4 minutes. Gently fold in the apple pieces.Fill and bake muffins:
Distribute the batter evenly among the prepared muffin cups. Bake at 425°F (220°C) for 5 minutes, then lower the temperature to 375°F (190°C) and continue baking for 20 minutes, or until a toothpick inserted in the center emerges clean.Cool muffins in pans:
Allow the muffins to cool in the pans for about 10 minutes, then move them to a wire rack to cool completely.