Position oven rack low in the oven, heat oven to 300°. Trim beef ribs of excess outer fat, careful to leave meat attached to the bone. Dry meat with paper towels, sprinkle with salt and pepper, and dust lightly with flour on all sides.
In a large Dutch oven or oven safe pot with a secure lid, heat the butter over med heat. Sear the ribs on all sides, adding more olive oil as needed. Reserve browned ribs on a platter.
Add onion, celery, carrots, mushrooms, red pepper, and garlic to the pot and cook until softened. Season with salt and pepper. Stir in the bay leaves, thyme, and parsley. Raise the heat and add the wine to deglaze the pan. Return the ribs to the pot and add the stock, and tomatoes. Stir to incorporate and make sure the meat is mostly covered. Bring it to a simmer, and drizzle with a little olive oil. Secure a lid on the pot and place in the preheated oven; cook for 4-41/2 hours.
Optional: Once ribs are fall-apart tender, remove from the oven and turn oven off. If desired, carefully skim any pools of fat on the top with a spoon and discard. Taste and add more salt and pepper, as needed. Stir-in couscous, replace lid and return to the oven (still off), for 10-15 minutes.
Serve over Mashed Cauliflower (as shown) with a side of skillet-seared asparagus.
It is important to use dry Marsala wine for this recipe rather than sweet Marsala.
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