Preheat your oven to 375°F (190°C) and prepare a muffin tin with paper cases or grease it generously.
In a large bowl, sift together 2 cups of flour, 2 teaspoons of baking powder, 1/4 teaspoon of salt, and 2 teaspoons of cinnamon.
In another small bowl, mix 2 teaspoons of flour with 1/2 teaspoon of cinnamon and coat the diced apples well.
In a separate large mixing bowl, cream together the melted butter, brown sugar, and caster sugar for about 2 minutes.
Add the eggs one at a time to the butter-sugar mixture, beating well after each addition, and then mix in the vanilla extract.
Gradually add the flour mixture to the wet mixture, alternating with milk, starting and ending with the flour mixture.
Fold in the cinnamon-coated apples gently without over-mixing the batter.
Step 8:
Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.
Bake the muffins for 20-25 minutes or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the tin for about 5 minutes, then transfer them to a wire rack to cool completely.