Bring sliced Beef to room temperature if using leftovers. If using raw beef slice and cook in large skillet. Remove to dish and set aside until the end.
In large skillet, melt butter as sliced mushrooms and 1/4 tsp kosher salt. Cook down for 10 minutes or so.
Add enough water to barely cover the mushroom over high heat bring to boil
Simmer until dry and add shallots. Cook until mushrooms are lightly browned.
Sprinkle with flour and cook 3 minutes to remove floury taste. Remove from heat and add booze if using.
Return to heat and cook until nearly dry. Add beef stock/broth . Cook until thickened over low heat do not boil.
When a desired consistency add sour cream(or yogurt)and beef. Combine well and heat beef thru.
Service over noodles of choice.