The white wine mustard sauce in this recipe comes straight from Ireland, and it's a decadent twist on the traditional mustard sauce, both savory and tart at the same time. This dish goes well with brown bread and butter.
In a medium-sized pot, boil the white wine, garlic, and onion for 5 minutes. Then, add the heavy cream and stock and simmer for 5 more minutes. Whisk in the mustard, salt, and pepper and simmer for 3-4 more minutes. Whisk in the flour and simmer until the sauce begins to thicken.
Place the corned beef in a large Dutch oven and cover with water. Add the chicken stock, parsley, and butter. Season with salt, to taste. Bring to a boil and skim off any foam, if necessary.
Reduce the heat, cover, and simmer until tender, about 4 hours. Meanwhile, place a steamer basket snugly inside a pot and add water until it reaches just below the steamer basket. Bring to a boil and add the cabbage to the basket. Cover with a lid and steam until tender.
Preheat the oven to 400 degrees.
Place the potatoes on a baking sheet or dish and roast in the oven until a fork pierces the center easily. Remove from the oven and set aside.
When the corned beef is tender, remove the parsley. Transfer the corned beef to a serving platter with the cabbage and potatoes. Ladle some hot cooking liquid over the corned beef and platter. Season with pepper, to taste. Serve immediately with 4 ounces of the mustard sauce.