Add the other 1 tbsp of butter to the pan and add the onions. Deglaze with a dash of water to lift off all the sticky bits leftover from the veal. Fry gently over a medium-low heat for 10 minutes until they’re translucent and beginning to go golden brown.
Add the carrot and celery and fry for another 5 minutes, then add the tomato puree. Cook out for a final 5 minutes before deglazing with the wine.
Return the veal to the pan with the bay leaf, thyme, cloves and saffron.
Pour over the chicken stock until it just covers the veal. Bring to a boil then turn down to a simmer. Simmer for 90 minutes, until the sauce has reduced and the veal is falling off the bone.