In a medium skillet, heat the avocado oil over low-medium heat until hot. Add the onions and caramelize until light brown, about 20 minutes. Add the wine and vinegar to the pan. Bring to a light boil and then lower heat to simmer for 20 minutes.

Place the brisket in a pan with enough depth for red wine sauce. Sprinkle meat on both sides with some salt and pepper. Pour the liquid over the brisket, cover with foil and marinate overnight in the refrigerator.

Preheat oven to 275 degrees Fahrenheit. Cook, covered, for two hours. Remove from oven and let the brisket cool. Slice against the grain, and then place back in the sauce.

Let the meat sit in the sauce for a few hours or overnight.

It freezes well if making ahead of time.

On day of serving, put defrosted brisket in preheated 275-degree oven and cook for 1 1/2 hours. If putting frozen brisket straight into oven, cook for 3 hours. It’ll be moist and easy to cut.