I have made this for years and my friends, family and co-workers love this. It's easy to make changes to this recipe and use what you have on hand. I've used green beans instead of peas. Chicken broth in the sauce if you're out of milk. Use bread crumbs, crushed up potato chips or croutons as your topping if you don't have Panko. Use cheddar cheese in place of the Parmesan cheese, just use what you have in your pantry and fridge.
Sauté mushrooms in 3-4 Tbls of butter and olive oil on medium heat in a large skillet. Add a little salt so they give off their water. After water is evaporated, add in chopped onions and sauté until onions are opaque and mushrooms are golden brown. Add in chopped garlic and sauté a couple more minutes. Set aside.
Boil noodles to al dente and and drain. Leave in about a cup of the pasta water in the pot with the noodles so they don't stick together while you're making the yummy sauce.
In a large Dutch oven add in 1/2 c butter and melt on medium heat. Sprinkle in flour and whisk until blended and cook for about a minute. It will be super thick, turn down to med/low. Slowly add room temperature milk and stir constantly. It will be thick and beautiful. Add more milk if it's too thick. Salt and pepper to taste. Add in room temperature cream cheese and half the parmesan cheese and whisk until combined. Season to taste. Add in noodles, frozen peas, mushroom, onions, garlic, and chopped or shredded chicken and stir until everything is coated. It should be very saucy. This makes a ton and you can easily split this into casserole pans and freeze one if you want to. I use the Pampered Chef 9X13 casserole pan. And it fills it to the top.
Combine the Panko bread crumbs with the rest of the Parmesan cheese and sprinkle on the top.
Bake 400 degrees 25 minutes or until bubbly. Turn on broiler and brown the top for about 5 minutes! Watch it close so they don't burn.