• Preheat the oven to 400°F
• Line 16 muffin cups with paper liners, or lightly grease if you don't have the liners.
• In a medium sized bowl, whisk together flour, baking powder, baking soda, salt.
• In a stand mixer with the paddle attachment, cream the butter and sugar together until light and fluffy.
• Add the eggs one at a time, mixing well after each addition.
• Add the vanilla and sour cream, mix until incorporated.
• Add the dry ingredients and mix on low until just blended.
• Stir in the apples and cinnamon.

Streusel Topping

• Mix together all the ingredients until crumbly.
• Sprinkle each muffin with the topping.
• Bake muffins 17 - 25 minutes or until a cake tester inserted into center comes out clean.
• Remove from oven and cool in the pan for 5 minutes.
• Remove from pan and finish cooling on a rack.