Toss the diced chicken with flour, salt, and pepper.
Brown the chicken in batches in a pan with oil.
Melt butter in the pan and sauté the onions, garlic, thyme, and celery salt.
Stir in more flour, then slowly add the chicken stock and milk, stirring to prevent lumps.
Bring the sauce to a gentle boil and let it thicken.
Add the lemon juice, mushrooms, and the browned chicken.
Simmer for 20 minutes until the chicken is tender.
Stir in the cream and let it bubble for 5 more minutes.
Serve the creamy chicken and mushroom casserole over mashed potatoes with green vegetables, garnished with parsley.
