Cut filet into 1/2 inch slices and, optionally, pound with a mallet until thin.
Cut filet again into strips one inch wide.
Place ghee in pan with medium high heat. Braise beef to wanted doneness.
Remove beef to plate, leaving any sauce behind.
Melt butter in pan and saute onion at low heat until sweet - maybe 40 min.
Add mushrooms, salt and pepper, and nutmeg and cook until mushrooms reduced in size. If using more
than low heat, keep close eye.
Add broth and raise temperature to boil off, stirring frequently.
While broth boiling down, cook egg noodles.
When reduced, add meat to heat, stir to warm but not cook more.
Turn off heat, tilt pan to collect juice, add sour cream and stir to blend, then
flatten pan and stir together.
Serve over egg noodles.