Preheat your oven to 180°C (350°F) and line a standard muffin pan with paper liners.

In a large mixing bowl, whisk together melted butter, granulated sugar, brown sugar, Greek yogurt, milk, eggs, vanilla extract, cinnamon, and kosher salt until smooth.

Gradually sift in the all-purpose flour, baking soda, and baking powder into the wet mixture, folding gently.

Fold in the chopped apples carefully.

Fill each muffin liner almost to the top with the batter.

In a separate bowl, combine flour, brown sugar, cinnamon, kosher salt, and melted butter for the streusel topping and mix until crumbly.

Sprinkle the crumble topping over each filled muffin liner.

Bake for 18–20 minutes, checking for doneness with a toothpick.

Allow the muffins to cool in the pan for at least 15 minutes before transferring them to a wire rack.