Place the vegetables, chicken, stock and seasoning in the inner pot of your crockpot (don't put the chicken all the way at the bottom or it might burn). Cover and cook on LOW for 6-8 hours.
Remove chicken and shred with two forks. Whisk flour into milk, then whisk in a ladle of hot broth from the crockpot. Pour this mix into the soup and stir well. Add the chicken back into the soup along with the noodles and stir. Cover and cook for 20-30 minutes, or until noodles are al-dente.
Stir in butter and check for seasoning. Add some salt and pepper if necessary and serve immediately.