Sauté Aromatics
Melt butter in a large skillet or pot over medium heat. Add onion and cook until soft. Stir in garlic until fragrant.
Make the Roux
Sprinkle flour over the onions and stir continuously for 1 minute.
Add Liquids
Slowly whisk in chicken broth, then milk. Stir until smooth and slightly thickened.
Cook the Pasta
Add uncooked pasta to the sauce. Reduce heat and simmer, stirring often, until pasta is tender.
Add Chicken & Veggies
Stir in cooked chicken and frozen vegetables. Simmer until heated through.
Season & Serve
Add thyme, poultry seasoning, salt, and pepper. Adjust seasoning and serve warm.