Add fat to a dutch oven or large sauce pot, then add vegetables, cook stirring often untill slightly caramelized, deglaze with the wine.
Add this mixture to a large work bowl with meat, cheese, egg yolk, salt n pepper, mix well.
If making meatballs, form meat into golf ball sized balls, if making a loaf use a greased loaf pan or free-form mold into a greased baking dish.
Cook meat in 350 degree oven for about 30 minutes, do not dry out the meat by cooking too long.
In sauce pot heat a little more oil, then cook onion and garlic, add sliced mushrooms, pureed mushrooms, stock, minced thyme, sour cream..heat to simmer....season with worcestershire sauce, adjust seasoning and thickness using potato flakes.
Serve meat with the sauce...garnish with fresh herbs.