Preheat oven to 375°F (190°C) and line a 12-cup muffin tin with paper liners.
In a large mixing bowl, whisk together flour, sugar, brown sugar, baking powder, baking soda, salt, and cinnamon.
In a separate bowl, whisk together melted butter, eggs, milk, sour cream, and vanilla extract until emulsified.
Incorporate the wet mixture into the dry ingredients using a rubber spatula, folding until just combined.
Gently fold the diced apples into the batter.
Divide the batter equally among the muffin cups.
Bake for 18 to 22 minutes or until a toothpick inserted into the center emerges clean.
Transfer to a wire rack and allow to cool for at least 10 minutes before serving.