Rinse and dry the knuckle slices. Cut the skin all around with a sharp kitchen knife, season the meat with salt and pepper. Heat clarified butter (I) in a heavy, shallow roasting pan. Sear the meat in it on both sides until golden brown. Pluck half of the thyme leaves and sprinkle over the meat.
Gradually deglaze with the stock (I): Always add just enough stock to dissolve the roasting substances. Always boil the liquid a second time. Steam the meat altogether in a closed roaster over medium heat for 1 1/2 hours.
Meanwhile, knead butter and flour together and set aside to cool. Peel the shallots and sauté all around in the clarified butter (Ii). Season with salt, pepper and sugar. Add stock (Ii) and sauté shallots for 10 min in closed saucepan at low temperature until soft, then remove from heat.
Remove the meat from the pot. Add the remaining stock to the roasting pan form and bubble, adding the flour butter in flakes with a whisk. Cook on low heat for 10 minutes. In the meantime, remove the meat and cut into bite-sized pieces, removing the bones, gristle and skin. Pluck the remaining thyme from the stems. Heat the meat and the shallots in the sauce, stir in the capers and sprinkle the thyme on top.
Tip: Instead of clarified butter, you can also use butter in most cases.