Sprinkle chicken with garlic powder, salt and pepper on both sides.

Heat oil in a large skillet over medium heat. Place chicken in skillet smooth side down.

Press down lightly with with spatula. Cook for 4 minutes until golden.

Turn and press lightly with spatula. Cook for 2 minutes.

Remove chicken onto a plate.

Turn heat up to medium high. Add butter, melt. Then add onions, cook for 1 minute, then add mushrooms.

Cook mushrooms until golden. Scrape bottom of fry pan to get all the golden bits off (this is flavour!).

Add flour, cook, stirring, for 1 minute.

Add half the broth while stirring. Once incorporated, add remaining broth.

Stir, then add sour cream and mustard. Stir until incorporated (don't worry if it looks split, sour cream will "melt" as it heats).

Bring to simmer,then reduce heat to medium low. Once it thickens to the consistency of pouring cream (3 minutes), adjust salt and pepper to taste.

Add chicken back in (including plate juices). Simmer for 1 minute, then remove from stove.

Serve over pasta or egg noodles, sprinkled with parsley or chives if desired.