Preheat the oven to 180℃.
Cook the macaroni according to package directions in salted boiling water. Drain and set aside.
In a separate frying pan, cook the bacon pieces or pancetta cubes until crispy and golden. Set aside.
Take a large saucepan and heat the butter. Add in the chopped onion and apple and sear for a few minutes.
Stir in the flour and slowly pour in the milk, a bit at a time, constantly stirring to stop lumps appearing. Add the salt and nutmeg.
Bring the mixture to the boil for a few minutes, then take off the heat.
Immediately stir in 1 cup of grated Gruyere cheese.
Stir in the chopped spinach and the cooked pasta.
Finally, add the cooked bacon pieces or pancetta cubes.
Empty the mixture into a greased oven dish.
Sprinkle 3 further tablespoons of grated cheese over the top and cook in the oven for 15 minutes or until golden.
Sprinkle with parsley to serve. Enjoy!