In a bowl or small food processor, combine the minced garlic, horseradish, honey, salt and pepper. By hand, rub this mixture all over the brisket, cover and refrigerate for at least 6 hours or preferably overnight.

Preheat the oven to 325 degrees F. Place the brisket in an enamel or glass pan with a tight fitting lid and and add the sliced onions. Pour the red wine or other liquid and cover the roasting pan tightly with a lid. Place the pan in the oven and roast, undisturbed, for 3 hours.

Uncover the pan and continue to roast for an additional hour, basting occasionally with the juices from the pan. Let it sit at room temperature for about 30 minutes before slicing.

Serve with additional horseradish.