Dredge sirloin in flour and then pan fry in batches, searing all sides. Set aside
In same skillet, sauté mushrooms in butter over high heat. Add to cooked meat.
In same skillet, sauté onions in olive oil until just tender. Add to meat mixture.
Deglaze pan with wine, scraping the bottom gently with a wooden spoon. Pour into a measuring pitcher and let cool. Add water if necessary to obtain 1 qt. of liquid. Whisk in gravy mix until lump free.
Bring 2 qt. of water to a boil. Whisk in slurry and bring back to a boil, cooking for 1 minute. Reduce heat and add meat mixture. Simmer for 15 minutes, stirring occasionally.
Remove from heat and stir in sour cream. Serve over cooked egg noodles.