Melt the butter and cook the onion in it until translucent. Add the chicken livers, shake the skillet, and cook over high heat until livers are browned. Do not overcook.
Reduce the heat, sprinkle the livers with parsley and thyme, and stir in the sour cream. Bring to a boil, stirring constantly. When the boiling point is reached, stir in the stock and simmer for about three minutes. Season with salt and pepper to taste and serve hot.