Pat thawed filet mignon tips dry with a paper towel.
Heat olive oil in a large braising pan; add filet mignon tips, shallots, onion, and garlic and cook until browned.
Add mushrooms, green onions, salt, pepper, and wine and allow to reduce by half over about 20 minutes.
Mix demi-glace, sour cream, and mustard in a small bowl until well incorporated.
Add to pan mixture and simmer until your desired thickness has been achieved.
Serve over optional cooked noodles or rice.