In a large skillet, melt the butter over medium heat. Add the mushrooms and cook, stirring occasionally, until golden brown, 5 to 7 minutes. Season with salt and pepper. Remove from the skillet and set aside.
Season the chicken with salt and pepper. Return the skillet to the stove, add the olive oil and increase the heat to medium high. Add the chicken, working in batches if necessary, and cook until it begins to brown on each side, about 5 minutes. Add the onions and cook until tender, 3 to 4 minutes. Stir in the flour and cook for an additional 2 minutes. Stir in the broth, scraping up any browned bits with a wooden spoon. Stir in the Worcestershire sauce, soup mix and cooked mushrooms. Reduce the heat to low and simmer until the broth is thickened to a gravy, about 7 minutes. Stir in the sour cream.
Serve over egg noodles with a dollop of sour cream and garnish with fresh chives.