Boil the potatoes with skins on in salted water until soft. (about 25 minutes).

Drain and when cool enough to handle, peel and press them through a potato ricer.

Boil the pasta in salted water until al dente.

Drain (reserve 1 cup of pasta water)

Peel and dice the onions.

Preheat the oven to 400F. Grease a casserole dish.

Heat the butter and oil in a large skillet.

Add the onions and cook until they start to caramelize.

Add the cream and bring to a boil.

Add 2+3/4 cups cheese and stir until a sauce forms.

Mix in the potato.

Mix in the chili crisp

Season with salt and pepper.

Add the pasta water and cook until combined

Mix in the pasta.

Transfer the mixture to the casserole dish.

Sprinkle the rest of the cheese over the top.

Bake for 25 minutes until a golden brown crust forms.

Remove from oven. Let stand for 10 minutes.

Chop the scallions into rings and garnish the dish with scallions and chili crisp before serving