Sauté Aromatics
Heat butter in a large skillet over medium heat.
Add diced onion and garlic, and sauté until softened and fragrant, about 2-3 minutes.
Make the Sauce
Sprinkle flour over the onions and garlic, stirring to combine. Cook for 1-2 minutes to remove the raw flour taste.
Gradually whisk in chicken broth and milk, stirring constantly until smooth.
Cook the Noodles
Add egg noodles to the skillet, ensuring they are mostly submerged in the liquid.
Cover and cook for 8-10 minutes, stirring occasionally, until noodles are tender.
Add Chicken and Vegetables
Stir in cooked chicken, frozen vegetables, thyme, salt, and pepper.
Simmer for 3-4 minutes, or until heated through and the sauce has thickened to your liking.
Garnish and Serve
Remove from heat and sprinkle with fresh parsley, if desired. Serve immediately.