Begin caramelizing the onions by adding the butter to a sauté pan, along with the onions and garlic over medium heat.
Season with salt and pepper, to taste.
Slowly cook the onions until they are softened and begin to slowly caramelize and turn brown; else, if cooked to quickly, they will develop a bitter flavor.
Slow cooking the onions will bring out their natural sweetness.; don’t rush this; let it take 15 to 20 minutes to complete the caramelizing process.
To a roasting pan, add all of the other ingredients and the caramelized onions.
Season with salt and pepper. if necessary.
Cover the roasting pan. with aluminum foil. as tightly as possible before adding the lid.
Place in the pre-heated oven for 4 hours or until the brisket is fall apart tender.
Skim the excess fat from the pan drippings and serve as au jus with the brisket or use it to make a gravy, whichever you prefer.
Notes
To complement the French Onion Braised Beef Brisket, serve with completecomfortfoods.com's recipe for Proper English Yorkshire Pudding: https://completecomfortfoods.com/proper-english-yorkshire-pudding/