Chop vegetables and saute in butter, but don't brown the onions.
Sprinkle with flour and then immediately whisk in milk or half and half. It should thicken like white gravy. Add more liquid as needed. You can also add in some cheese for extra creaminess. Sometimes, I add the broccoli at this point to make things easy.
Combine gravy and cooked noodles and other ingredients in a bowl.