In a medium bowl, whisk together milk, flour, onion powder, salt, pepper, paprika, garlic powder.
In a 5-quart saucepan, cook butter, garlic and onion together until onion is soft.
Add chicken broth and chicken base to the saucepan, whisk to combine and bring to a boil.
Once the mixture is boiling, add the milk mixture and cook over medium-high heat until thickened (1-2 minutes).
Pour sauce over the chicken/vegetable/rice mixture.
Bake at 350 for 25-30 minutes or until cooked through.