In my opinion, brisket is best made in advance, which is especially useful when cooking for several days of Yom Tov. It freezes beautifully, too! Just cook, cool, slice and return to sauce. As the sliced brisket sits in the sauce, it absorbs the flavor and becomes super soft!
In a small saucepan, heat the avocado oil over low-medium heat. Add the shallots to the pot and cook until soft and begin to caramelize (about 25 to 30 minutes). Add the wine, vinegar, and salt to the pot. Bring to a boil and then lower to a simmer for 20 minutes.
Place the brisket in a nine- by 13-inch pan. Pour the sauce over the brisket. Cover with foil and place in the fridge to marinate overnight.
Preheat oven to 275 degrees Fahrenheit. Cook, covered, for two-and-a-half hours. Remove from oven and let the brisket cool. Slice against the grain, and then place back in the sauce.
Let sit in the sauce for a few hours or overnight. Freeze if making more than two days in advance.