Heat your oven to 275ºF.
Place the ribs in a deep ovenproof tray or dish and cover with cold water. Add the garlic, carrot, celery, thyme, cloves, anise and bay leaves, and cover with aluminium foil.
Roast in oven for two and a half hours, until the rib meat is very tender, but not quite falling from the bone. Check on the ribs two or three times during cooking, and skim off any scum that rises to the surface of the liquid in the tray. When the ribs are cooked, remove them from the oven and leave to cool down in the cooking liquid.
For the glaze, cut the quince paste into small pieces and place with the vinegar in a saucepan over a low heat. Melt the quince paste gently, stirring occasionally. You will end up with a thick jamlike glaze.
Remove the cooked ribs from the liquid and pat dry. Place on a tray and brush them all over with the glaze, saving some of the glaze for basting later.
Heat your barbecue to 350ºF, and cook the ribs for three to four minutes on each side, until caramelised. Brush the remaining quince glaze on the ribs. Season with sea salt and serve hot.