To make the bacon lardons: add the bacon pieces to a cold frying pan and turn on the heat to medium heat. Cook lardons, stirring regularly, until the fat renders and the bacon is browned and crispy, about 8 to 10 minutes. Remove lardons with a slotted spoon and drain on a paper towel-lined plate.
To make the caramelized onions: In a frying pan over medium-low heat melt the butter. Alternatively cook the onions in 2 tablespoons bacon fat if you are cooking bacon lardons for the garnish (just use the same frying pan and remove all but 2 tablespoons of the fat from the pan). Add the onions, season with salt, and cook, stirring regularly until soft and golden, about 30 minutes. Set aside.
To make the applesauce: Place the apples in a saucepan with water and cover. Simmer gently on medium-low heat, stirring once or twice, until the apple is completely tender, about 20 minutes. Mash with a fork until smooth. Set aside.
To make the macaroni: Add the cubed potatoes to a large pot and cover generously with salted water. Bring to a boil, add the macaroni and continue to cook until the macaroni is barely al dente and the potatoes are tender. The exact time will depend on the macaroni shape. It’s about 10 minutes for ziti. If using a smaller shape with shorter cook time (like elbows which need only 6 minutes for al dente) you may want to boil the potatoes for a couple minutes on their own before adding the macaroni. Drain the macaroni and potatoes.
Return to the drained macaroni and potatoes to the pot, add the cream and return to medium heat. Stir until the cream starts to heat up (a minute or so) and then add the grated cheese, a little salt, and a bit of freshly grated nutmeg. Keep stirring until the cheese has melted into a thick and luscious sauce.
Serve the cheesy Alpine macaroni on individual plates topped with caramelized onions, crispy bacon lardons (optional), and with applesauce on the side to eat either with the macaroni or afterwards as dessert based on personal preference.