5 tsp olive oil
1 medium onion, sliced
a bunch of fresh mushrooms -- I used 2 big portabellos, 8-10 shitakes, and a small pack of regular white button mushrooms
1 15-oz can fat-free beef broth
1 Tbsp corn starch
1/4 cup cold water
1 tsp dijon mustard
1/2 cup fat-free sour cream
Cooked egg noodles or rice
Heat olive oil in a large skillet over medium-high heat, then add onion, stirring and cooking until browned and soft/translucent. Remove onion from pan and set aside. Add mushrooms and cook several minutes, until soft and brown. Remove from pan and set aside. Pour beef broth into pan over high heat and bring to a boil, stirring to get all the yummy cooked bits from the bottom of the pan. Boil for several minutes, until broth has reduced by about one half.
Meanwhile, whisk together corn starch and water until no lumps remain. Return mushrooms and onion to pan, stirring until heated through. Push mushrooms and onions off to the sides of the pan, leaving the liquid in the center. While stirring constantly, pour the corn starch/water mixture into the boiling beef broth. It will very quickly thicken up. Reduce heat to medium-low and stir in dijon mustard and sour cream. Serve over cooked egg noodles or rice.
Note: To make this recipe vegetarian, substitute vegetable stock for the beef broth, and add some soy sauce for color.