Preheat the oven to 400 degrees F.
Bring 1 1/2 cups water to a boil in a pot and season with salt. Add the cauliflower, cover and steam until just tender, 7 to 8 minutes. Drain
and cut into florets.
Meanwhile, bring another pot of salted water to a boil and cook the noodles to just shy of al dente
, about 5 minutes. Drain.
Heat 4 tablespoons butter
in a large skillet over medium heat. Add the mushrooms and cook until tender and browned. Add the garlic and shallots
and cook, stirring, for 2 to 3 minutes. Add the flour and cook, whisking, for 1 minute. Deglaze
with the sherry, stirring and scraping up any browned bits with a wooden spoon. Whisk
in the chicken stock
and bring to a boil. Reduce the heat to a simmer
and cook for a few minutes, then stir in the heavy cream
. Season with salt, pepper and a few grates of nutmeg
Combine the cauliflower
, noodles, chicken and sauce
. Transfer to a casserole dish
the remaining 4 tablespoons butter in small pan, then drizzle
over the panko
in a bowl and toss to combine. Add the Parmigiano-Reggiano and toss. Sprinkle the breadcrumbs
over the casserole. Bake until hot, bubbling and golden, 40 to 45 minutes. Sprinkle with the parsley. Divide among plates.
Cook's Note: The unbaked casserole (without the breadcrumbs) can be covered and refrigerated for a make-ahead meal.