Preheat oven to 424.4 F (218C) and adjust the rack to use the middle and low positions. Line a 12-cup muffin pan with muffin liners.
Prepare 2 mixing bowls; one for dry and another for wet ingredients.
Dry ingredients: In the first bowl, except for the raisins and apple pieces, add and mix the dry ingredients, whisking to combine. Once combined, add the raisins and apple pieces on top, then set aside.
Wet ingredients: In the second bowl, mix all the wet ingredients together, and whisk until well combined.
Combine wet and dry ingredients: Pour the wet ingredients into the dry ingredients bowl. Using a spatula, fold the wet and dry ingredients together gently; don't over-mix. (It's OK to have some lumps and dry flour still showing in the batter, it is normal and helps to make light and fluffy muffins.
Fill pan: Fill around 2/3 of each muffin liner with the batter (around three scoops each) and sprinkle some granulated sugar on top of each muffin for extra crunch.
Bake for muffins 20 minutes or until golden brown. You can also check with a skewer, insert it into the middle, and if it comes out clean, they’re ready.
Cool: Leave the muffins in the pan for 5 minutes to cool down slightly before removing them onto a cooling rack.