01 - Preheat oven to 375°F and grease a 9x13-inch baking dish.
02 - Boil egg noodles in salted water for 2 minutes less than package directions. Drain and set aside.
03 - Blanch fresh broccoli florets in boiling water for 2–3 minutes until just tender, then drain; if using frozen, thaw and drain well.
04 - Melt butter in a large skillet over medium heat. Sauté chopped onion for 3 minutes until softened. Add minced garlic and cook for 1 minute longer.
05 - Combine cooked noodles, chicken, broccoli, sautéed onion and garlic, cheddar cheese, milk, sour cream, cream of chicken soup, salt, pepper, and thyme in a large bowl. Mix thoroughly.
06 - Spread mixture evenly in the prepared baking dish.
07 - In a small bowl, mix panko breadcrumbs with melted butter. Stir in additional cheddar cheese if preferred. Sprinkle topping evenly over assembled casserole.
08 - Bake uncovered for 30 to 35 minutes, until the top is golden and contents are bubbling. Let rest for 5 minutes before serving.