Preheat oven to 325 degrees Fahrenheit (160 degrees Celsius).

In a large Dutch oven, set over medium-high flame, heat two tablespoons oil. Add the brisket and brown on both sides for three to four minutes each side. Remove meat and set aside.

Remove the Dutch oven from the heat and arrange onions and garlic along the bottom. Add three tablespoons blending flour. Mix to coat. Add the wine, bay leaves, and brown sugar if using.

Combine the mustard powder and remaining one tablespoon flour in a small bowl. Rub the top and sides of the meat with the flour combination and cover with the oil, smearing it onto the meat to create a paste. Sprinkle generously with freshly ground black pepper and season generously with kosher salt.

Cover and bake for about one and a half hours. When done, remove the bay leaves. Allow the meat to cool to room temperature and then refrigerate overnight, or until thoroughly cool. Skim off the fat if desired.

Slice the meat to desired thickness, cutting against the grain to ensure nice, even pieces. Spread the gravy completely over the meat before reheating. Reheat in a 300 degrees Fahrenheit (150 degrees Celsius) oven for at least one hour, and up to two hours.