Peel the onions, celery and carrot, and cut everything into slices. Heat the extra virgin olive oil in a pan, add the chopped vegetables and sautè for about 5 minutes over medium-high heat, then add the white wine and cook for another 10 minutes.
Add also the butter in the pan with the oil and and melt it. Now take the ossobuco and, using a pair of scissors, make 3 incisions on the connective tissue of each to prevent them from curling in cooking. Flour the ossibuco from both sides and beat them gently to remove excess flour. Place the ossobuco inside the pan, add the tomato paste, salt and pepper, sauté over medium-high heat without touching it. After about 4 minutes, turn it gently and you will notice that everything is made up of a delicious crust.
Brown the ossobuco on the other side for about 2 minutes. At this point, start adding the broth so that it almost covers the meat and lower the heat, cover with a lid and cook a medium-low heat for 35 minutes. Add the broth litlle by little if you see that it is missing.
After 35 minutes of cooking, turn the ossobuco very gently, copy again with the lid and continue cooking for another 25 minutes. Your ossobuco is ready!