Pre heat oven to 150c/300f.
Heat olive oil in a heavy based pot/dutch oven (with lid) over medium high heat, brown the shanks (4) well all over and then remove to a plate.
Carefully drain excess oil from the pot leaving about 1 tbsp, then add sliced onions (2 medium) to the same pot and fry onions over medium low heat until they start to soften.
Sprinkle plain flour (1½ tbsp) over softened onions, and stir over medium low heat for a minute.
Add crushed garlic (3 cloves), sweet paprika (1½ tsp), ground cumin (1½ tsp), ground coriander (1½ tsp), ground cloves (¼ tsp) and cinnamon (⅛ tsp) to onions, and continue to fry for another minute.
Then add tomato paste to onions, and fry for another minute. Add beef stock (3 cups) and orange juice (from 1 orange - approx ⅓ cup) and salt (½ tsp) to onion mixture and mix well, scraping up any flavour spots from the bottom of the pot.
Return shanks to pot (see my notes) and bring to a simmer, place the lid on and transfer to the oven to bake for 3 hours or until cooked through and falling away from the bone. Stir orange zest (from 1 orange) through sauce and serve.