1. Cut the heart into three or so large pieces that can be laid flat in your pot.
2. Place the pot over high heat and add the oil. Brown the pieces of heart on both sides, about 3 minutes per side.
3. Remove and set aside.
4. Turn the heat to medium and add the onions and cook until softened but not brown, about 5 minutes.
5. Add the heart back to the pot, along with the rest of the ingredients. The heart should be covered halfway by the stock.
6. Add more water if needed.
7. Let the stock come to a simmer.
8. In the meantime, preheat your oven to 300 F. Lay a piece of parchment paper over the heart and put the lid on the pot. Braise in the oven until the heart is tender, at least 2 hours.
9. Let the heart cool slightly in the liquid. At this point, the braise may be refrigerated and reheated when you are ready to eat. When you are ready to serve, remove the heart from the liquid and place the pot over medium-high heat. Reduce the liquid until you have a cup or so remaining of the liquid.
10. Cut the braised heart into slices and spoon the sauce over the heart.
11. Serve with couscous and the braised root vegetables in the pot.