Melt butter and bacon grease in a large dutch oven over medium heat, add chopped onions and sauté until golden brown and caramelized. Approximately 30 minutes.
While onions are cooking slice and season beef, set aside.
Once onions are caramelized add herbs, salt and pepper. Sauté until fragrant.
Remove onion and herb mixture from pot and set aside.
Add vegetable oil to pot over medium high heat. Add beef strips to pot in a single layer until nicely browned on each side. Work in small batches until finished.
Remove beef from pot and deglaze pot with red wine scrape all browned bits on bottom of pan.
Add the onion mixture and beef back to the pan. Pour in enough beef stock to cover all ingredients. Cover with a lid and transfer to a 300°F oven for 1 hour, or simmer gently on the stovetop for up to 2 hours, until the beef is tender. Check for tenderness after 1 hour if using the oven, or continue simmering on the stovetop as needed.
Once beef is tender, slice mushrooms and sauté with butter in a separate pan. The mushrooms should be tender and golden brown.
Add mushrooms to pot with beef and onions.
In the pan you cooked the mushrooms make the roux. Melt the butter and add flour mixing continuously for a few minutes to cook the flour.
Take 1/2 cup of the cooking liquid from the pot and slowly add to roux while mixing. Add mixture to pot stirring constantly until sauce has thickened. Bring sauce and beef to a boil then lower heat to simmer gently.
Turn off heat and add sour cream to the sauce when it is no longer boiling. Mix until completely incorporated.
Seas to taste and served over buttered noodles or your starch of choice.