Add one tablespoon butter to a large pot or dutch, once melted add in chicken pieces. Cook thoroughly.
Once cooked, transfer to a plate. Drain any liquid from the pot.
Add the other tablespoon of butter. Add the onion and cook over moderate heat, stirring, until softened, about 3 minutes.
Add the mushrooms, stirring occasionally, until softened and lightly browned, about 7 minutes.
Add the garlic, bay leaves and thyme and cook until fragrant, about 1 minute.
Pour in the wine and cook until at least half-evaporated, about 10 minutes.
Add the chicken broth and simmer until reduced by half, about 15 minutes.
Remove the pot from the heat and stir in the sour cream, Greek yogurt and milk. Stir well.
Add the chicken to the sauce and simmer until heated through.
Season with salt and pepper.
Stir in the celery leaves.
Remove the bay leaves and thyme sprigs.
Serve and enjoy!