Step 1Stem the spinach and wash it thoroughly. Drain.
Step 2Place a large, heavy-bottom pot over high heat and add the olive oil and spinach. (You may need to add in batches, stirring until each batch wilts before adding the next.)
Step 3As soon as any remaining water has evaporated from the leaves and they just begin to fry, lower the heat. Gently cook the leaves, stirring frequently. (If they burn, the dish must be started over again.) Cook the leaves until they are of an almost jam-like consistency and are greenish-black in color (this is called the "black gold" stage), about 1 1/2 to 2 hours (timing will vary depending on the heat of the oil and thickness of the pot).
Step 4Remove the pot from the heat. Strain the spinach from the oil, and place the spinach in a bowl. To the oil in the pot, add 2 quarts water, the beans, onion, garlic, mint, cinnamon and black pepper. Stir in the calf's foot if using.
Step 5Bring the mixture to a boil over high heat. As soon as it comes to a boil, stir in the spinach and beef, then reduce the heat to a gentle simmer and cook, uncovered, until the meat is fork-tender, 2 to 2 1/2 hours. (The liquid level will reduce as the t'fina cooks and should ultimately have a sauce-like consistency; if the liquid evaporates too quickly, add additional water as needed until the meat is tender.)
Step 6Meanwhile, make the couscous: Place the couscous in a large shallow glass baking pan and stir in 1 tablespoon salt and the canola oil. Spread the couscous into a thin, even layer, then pour over the 2 cups boiling water and cover tightly with plastic wrap. Set the couscous aside for 5 to 10 minutes until the water is absorbed, then uncover and fluff the couscous gently with a fork. Set aside in a warm place until the t'fina is ready.
Step 7When the meat is tender, stir in the sausage and remaining teaspoon salt. Continue to cook the t'fina until the sausage is cooked through, 10 to 15 minutes. Strain any excess oil from the pan and discard. Season to taste with additional salt if desired.
Step 8On a large plate or platter, mound the couscous. Using a slotted spoon, plate the t'fina on another platter (a deep, pasta-style platter) with the meat, sausage and optional calf's foot arranged on top. Spoon additional sauce, as desired, over the dish. Serve immediately.