03Combine the garlic paste and green onions in a small bowl. Spread half of the mixture over the brisket. Flip the meat and add the remaining mixture to the other side. Set aside.04In the same pot, over low heat and add the parsnips. Season them with a little salt and a scant 1 tablespoon brown sugar. Stir to coat with the oil and cook until slightly tender, about 2 to 3 minutes. Add in 2 tablespoons apple cider vinegar and the leeks and gently brown them, about 3 to 5 minutes. Adjust the seasonings with salt. Pour in the wine and let it reduce for 5 minutes. Sprinkle the vegetables with the remaining 1/4 cup of brown sugar and another pinch of salt. Cook them until browned, another 3 to 5 minutes.05Add the brisket to the pot and stir in 2 to 3 cups of the beef stock. Bring the stock to a gentle simmer. Slide it into the center of the oven and cook for 1 hour. Check the level of the liquid, adding water, if needed. Remove the pot from the oven, taste and re-season, if needed. Return the pot to the oven and cook the brisket until the meat is tender when pierced with a fork, an additional 1 to 1 1/2 hours (see Cook's Note).06Remove the pot from the oven and transfer the meat to a platter. Arrange the vegetables alongside and ladle the sauce on top.