Preheat oven to 375 degrees and spray a muffin tin generously with cooking oil. Set aside.
Start with the crumb coating: In a small bowl, mix together flour, brown sugar, and instant oats.
Cut the cold butter slices into the mixture either using a pastry cutter or a fork.
Once the mixture has a “crumbly” consistency, wrap with plastic and refrigerate.
To make the muffins, start by sifting together flour, baking powder, salt, cinnamon, and nutmeg.
In a separate bowl, whisk together sugar, eggs, and butter.
Slowly add dry ingredients into the egg mixture, alternating with the cup of milk.
Fold chopped apples into the batter.
Scoop the muffin batter into coated muffin tin, filling it about ¾ of the way.
Remove crumble from the refrigerator and top each muffin with a generous amount.
Bake for 17 to 20 minutes or until completely cooked through.
Remove from oven and allow to cool for 10 minutes on a wire rack. Serve and enjoy!