In a large pot of salted boiling water, cook the diced potatoes for about 5 minutes.
Add the macaroni to the pot with the potatoes and cook according to the pasta package instructions until both are tender.
Drain and return the potatoes and pasta to the pot.
In a saucepan, heat the heavy cream and milk over medium heat until just about to simmer.
Add the shredded Gruyère cheese to the cream mixture, stirring until melted and smooth.
Season with salt and black pepper to taste.
In a skillet, melt the butter over medium heat.
Add the thinly sliced onions and cook until golden brown and caramelized, about 15-20 minutes.
Pour the cheese and cream mixture over the potatoes and pasta, stirring gently to combine.
Add the caramelized onions to the pot and mix well.
Transfer the Älplermagronen to a serving dish.
Garnish with fresh chopped parsley.
Enjoy your meal!