Step 1: Preheat the Oven : Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease lightly with butter.

Step 2: Prepare the Crumb Topping : In a small bowl, combine flour, brown sugar, and cinnamon. Add cold butter cubes and use your fingers or a pastry cutter to mix until crumbly. Place in the fridge to chill while preparing the muffin batter.

Step 3: Mix Dry Ingredients : In a large bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg.

Step 4: Combine Wet Ingredients : In another bowl, whisk together brown sugar, granulated sugar, oil, eggs, milk, and vanilla extract until smooth.

Step 5: Mix the Batter : Add the wet mixture into the dry ingredients. Stir gently until just combined — do not overmix! Fold in the chopped apples evenly.

Step 6: Fill Muffin Cups : Spoon the batter evenly into the prepared muffin tin (fill each about ¾ full). Sprinkle a generous amount of crumb topping over each muffin.

Step 7: Bake : Bake for 22–25 minutes, or until golden brown and a toothpick inserted in the center comes out clean. Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Step 8: (Optional) Add Cinnamon Glaze :Whisk together powdered sugar, milk, and cinnamon until smooth. Drizzle over cooled muffins for a sweet finishing touch.