Preheat the Oven: Preheat your oven to 180°C (350°F). Line a muffin tin with paper liners or grease it with butter.

Make the Muffin Batter:

In a large bowl, whisk together the flour, baking powder, baking soda, salt, and ground cinnamon.

In another bowl, mix the granulated sugar, brown sugar, melted butter, eggs, vanilla extract, and milk until well combined.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Be careful not to overmix.

Fold in the diced apples gently.

Prepare the Crumb Topping:

In a small bowl, combine the flour, brown sugar, and cinnamon for the topping.

Add the softened butter and mix with a fork or your fingers until the mixture resembles coarse crumbs.

Fill the Muffin Cups:

Divide the muffin batter evenly among the muffin cups, filling each about 3/4 full.

Sprinkle the crumb topping generously over each muffin.

Bake the Muffins: Bake in the preheated oven for 18-22 minutes or until a toothpick inserted into the center comes out clean.

Cool and Serve: Allow the muffins to cool in the pan for a few minutes before transferring them to a wire rack to cool completely.