Trim unwanted fat from the leftover prime rib.Slice the beef into 1" x 2" pieces.Reserve aside until ready to use.
Preparing Ingredients for the Sauce
Saute the Onions in the vegetable oil over medium high heat until translucent.
Add the Mushrooms and saute until they begin to sweat about 1-2 minutes.
Add the Dijon Mustard and saute to combine with the Onions and Mushrooms. Allow the mustard to toast in the pan to develop depth of flavor.
Add the butter, melt and mix to combine with vegetables and mutard.
Add the flour and mix to combine in the pan to make a roux.
Add the Beef Broth in ½ cup increments. Whisking to combine and break apart the roux. Between each addition of liquid.This is the opportunity to break down the roux.
Once the roux has broken apart, add the remaining broth.
Add the Worcestershire Sauce.
Bring the sauce to a boil and reduce to a simmer.
Add the sliced Prime Rib to the pan.
Simmer the sauce with the beef until thickened and the beef has been heated.Approximately 2-3 minutes.
Cook the Egg Noodles and drain.I do not recommend adding oil to the cooked egg noodles. The sauce will adhere to the noodles better.Plate the Prime Rib Beef Stroganoff over the cooked Egg Noodles.Garnish with a tablespoon of sour cream and a dash of Paprika if desired.