Preheat your oven to 375°F and prepare a 9x13 baking dish by lightly buttering the bottom and sides. Cook the egg noodles according to package directions, drain, and set aside for later assembly and baking.

Heat butter in a large skillet over medium-high heat until foaming, then add chicken pieces and cook for 5-7 minutes until golden on all sides. You don't need to cook the chicken through completely since it will finish cooking in the oven. Remove the chicken and set on a clean plate.

In the same skillet, sauté diced onion and sliced mushrooms for about 4 minutes until softened and fragrant. Add minced garlic and cook for one more minute until the aroma fills your kitchen.

Pour in the chicken broth, scraping up any browned bits from the bottom, then stir in heavy cream and sour cream until completely smooth. Add thyme, rosemary, salt, and pepper, stirring gently to combine all creamy hearty chicken casserole flavors evenly throughout the sauce.

Return the chicken pieces to the skillet, reduce heat to low, and simmer for 5 minutes to infuse the meat with flavor. Gently fold in the cooked noodles and frozen peas, being careful not to break the tender pasta strands.

Transfer everything to the prepared baking dish, spreading evenly across the bottom. Sprinkle panko breadcrumbs mixed with fresh parsley over the top for a golden, textured crust that bakes beautifully.

Bake uncovered for 25-30 minutes until the sauce is bubbly around the edges and the breadcrumb topping turns golden brown. Let rest for 5 minutes before serving to allow flavors to settle and sauce to thicken slightly.