Slow Cooker Chicken Wild Rice Soup

onion ((chopped))

medium carrots ((peeled and chopped))

large stalks celery ((chopped))

cooked chicken ((shredded) (300g))

wild rice ((uncooked ) (170g))

mushrooms ((stems removed and sliced) (225g))

dried thyme

chicken stock (/ broth (1.9 liters))

milk ((240 ml))

butter ((4 tbsp/56g))

all-purpose flour ((75g))

water ((240ml))

Salt (and pepper)

parsley ((chopped) (25g))