In a large skillet melt 2 tablespoons of the butter over medium-high heat. Add cubed chicken and sprinkle generously with salt and pepper. Cook until browned, about 3 minutes per side. Remove chicken from pan and set aside.

Once the chicken is about done, get the noodles started cooking, aiming to have them ready at the same time the sauce is ready. Boil in a large pot according to package directions. Drain and set aside.

Meanwhile, melt remaining 2 tablespoons of butter in the skillet and reduce heat to medium. Add mushrooms and onions and cook until tender, about 5-6 minutes, scraping up the browned bits on the bottom of the pan. Add garlic and cook for 1 minute more. Sprinkle with flour and stir until combined.

Add chicken broth and return heat to medium-high. Bring just to a boil and simmer until thickened, stirring frequently, about 2-3 minutes. Stir in sour cream and season with salt and pepper.

Add chicken and noodles to pan and stir until combined. Stir in most of the chopped chives, reserving some to garnish on top. Serve immediately and store any leftovers in the fridge.