Make the apple pie filling

• Peel, core and dice the apples into bite-sized pieces.
• In a saucepan, combine the apples, sugar, cinnamon, nutmeg, flour and lemon juice.
• Cook over medium heat, stirring occasionally, until the apples soften and the filling thickens; stir in the butter if using, then remove from the heat and let cool.

Make the crumble topping

• In a small bowl, mix the flour and sugar.
• Add the cold diced butter and rub it in with your fingers until crumbly. Set aside.

Make the muffin batter

• In a large bowl, whisk together the flour, sugar, baking powder, cinnamon, nutmeg and salt.
• Mix in the chopped apple.
• Add the milk, egg, vanilla extract and melted butter, mixing until smooth without overmixing.

Chill the batter

• Cover and chill the batter in the refrigerator.

Preheat and prepare the tin

• Preheat the oven to 180 °C (350 °F).
• Line a muffin tin with paper liners.

Fill the muffins

• Spoon the batter into the muffin tins, filling each about three-quarters full.
• Add a spoonful of apple pie filling to each muffin.
• Sprinkle the crumble topping generously over each muffin.

Bake the muffins

• Bake until a toothpick inserted in the center comes out clean.

Cool and serve

• Let cool in the pan, then transfer to a wire rack to cool completely.
• Serve and enjoy.