Peel and chop the apples into small ½-inch pieces.
In a small bowl, combine the brown sugar, granulated sugar, melted butter, and all-purpose flour. Mix until a crumbly topping forms.
Add the softened butter, brown sugar, and granulated sugar to a mixing bowl. Beat with an electric hand mixer until light and creamy.
Add the eggs and whisk until well combined.
Add the yogurt or sour cream and mix until smooth.
Add the vanilla extract and milk, then whisk until fully incorporated.
In a separate bowl, whisk together the all-purpose flour, baking soda, baking powder, ground cinnamon, and salt.
Gradually add the dry ingredients to the wet mixture and mix until just combined.
Add the chopped apples and gently fold them into the batter.
Line a muffin tin with paper liners.
Divide the batter evenly among the muffin cups.
Sprinkle the prepared crumb topping generously over each muffin.
Bake 15-20 min until the muffins are golden and a toothpick inserted into the center comes out clean.
Let the muffins cool in the pan for a few minutes.
Transfer the muffins to a wire rack, let them cool completely, then serve and enjoy.
