Sous vide chicken at 150 for 1-1.5 hrs (can go up to 4 hours); OR bake the chicken: Preheat the oven to 425°F. Line a baking sheet with foil for less cleanup. Place chicken thighs on the baking sheet, sprinkle with salt and pepper on both sides (and/or seasoning of choice) and bake for 18-23 minutes, depending on the size of the thighs
When the chicken is finished, slice it into cubes.
Preheat the oven to 350 degrees F.
Cook and drain spaghetti according to package instructions.
While the spaghetti is cooking and the oven is preheating, in a medium saucepan, melt butter over low heat. Stir in flour, salt and pepper. Cook, stirring constantly, until mixture is smooth and bubbly; remove from heat.
Stir in broth and milk. Heat to boiling, stirring constantly. Boil and stir for 1 minute.
Stir in sherry, spaghetti, chicken, and mushrooms.
Into an ungreased 2-quart casserole, pour the spaghetti mixture.
Sprinkle cheese evenly over the top.
Bake uncovered for about 30 minutes or until bubbly in the center.