Preheat oven to 180C. Heat olive oil in a casserole dish. Finely chop three onions and three garlic cloves and add to the oil with the thyme and bay leaves. Season with salt and pepper. Cook until onions are soft and have started to colour,about 20 minutes. Add tomato paste and cook a further five minutes.
While onions are cooking,heat a frypan with a little vegetable oil,dust osso bucco in lightly seasoned flour and brown on both sides. Add beef stock to onions and bring to the boil. Add meat and cover with a lid. Bake in the oven for two hours or until osso bucco is tender and falling off the bone.
To make the pilaf,finely chop the remaining onion and one of the remaining garlic cloves. Melt butter in a saucepan,add onion and garlic,and season. Gently cook until soft,about 10 minutes. Add risoni and chicken stock,bring to the boil and cover with a lid or tightly wrapped foil. Bake in the oven for 30 minutes.
To make the gremolata,finely chop the last garlic clove,parsley and lemon rind and mix together. Sprinkle on top of osso bucco just before serving with the pilaf.