Cook the macaroni in well-salted water until al dente (slightly undercooked). Drain and set aside, it will finish cooking in the oven.

Heat olive oil in a large pan and add the sliced onions with a pinch of salt. Cover with a lid and cook on medium heat (level 6/9), stirring occasionally. Let them slowly caramelize for a deep, sweet flavor, this can take quite a while.

For a faster version, add small splashes of water as needed to prevent sticking, and optionally a pinch of sugar to speed up browning. Cook until soft, jammy, and deeply golden.

Set aside and divide the onions in half.

In a saucepan, melt the butter over medium heat. Add the flour and cook for about 1 minute, stirring constantly. Gradually pour in the heavy cream and milk, whisking until smooth.

Season with salt, pepper, garlic powder, paprika, and a pinch of nutmeg. Let the sauce simmer gently until slightly thickened.

Mix all three cheeses together. Add half of the cheese mixture to the sauce and stir until melted and smooth.

Add the cooked macaroni and half of the caramelized onions to the sauce and mix well.

Transfer the mac & cheese to a baking dish. Top with the remaining caramelized onions and sprinkle over the remaining cheese.

Bake at 180°C (top/bottom heat) for 30 minutes, until bubbly and lightly golden on top.