• Preheat oven to 425° F. Spray 12 cups of a muffin pan with non-stick cooking spray or line with paper muffin liners. Set aside.

Crumb Topping

• In a small bowl, add the flour, brown sugar, granulated sugar, and cinnamon.
• Cut in the butter until the mixture is crumbly, A fork or pastry cutter work well for this step.

Apple Muffins

• In a large mixing bowl, use an electric mixer to beat together the softened butter, brown sugar, and granulated sugar until smooth.
• Add the eggs, sour cream, milk, and vanilla extract and mix until well combined.
• In a separate mixing bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt.
• Add the dry ingredients into the wet ingredients and mix together just until everything is incorporated.
• Fold in the pieces of diced apple.
• Scoop the muffin batter into the cups of the prepared muffin tin, filling each to the top. An ice cream scoop works great for muffins!
• Spoon the crumb topping evenly over all of the muffins.
• Bake the muffins at 425° F for 5 minutes, then reduce the oven temperature to 350° F. Continue to bake for an additional 15-18 minutes until a toothpick inserted into the center comes out clean.
• Remove the muffins from the oven and cool in the pan for 5 minutes. Remove and cool the muffins completely on a wire cooling rack.