1Peel the onions and garlic, and cut them in half. Brown them slightly in butter and add in the tomato paste. Stir well, and sauté with the onions for a few minutes — this will remove some of the acidic tang from the paste. Transfer the onion mixture into a slow cooker.
2Brown the oxtail - season with salt and pepper.
3Wash and julienne the orange peel with a zester or a potato peeler. Juice the orange, and mix juice and orange peel into the oxtail along with the crushed tomatoes, vinegar, bay leaves, Italian seasoning , oregano.
4Place the meat into the sauce, and deglaze the sauté pan with 50 ml water; pour the resulting sauce over the stew.
5Cook on low in the Slow cooker on low for about 7 to 8 hours