Peel, if necessary, and finely chop carrot, celery, onion and two of the garlic cloves. Place them in a large pot, add the olive oil and brown, on a medium/low heat, for about 15 minutes. 

Add chicken, tomato, rosemary, sage and the other two, unpeeled, garlic cloves. Cover and cook, lid on and over medium heat, for an hour (until the meat easily comes away from bones).

Remove the chicken legs, rosemary, sage and the garlic cloves (to tell the truth, I didn’t find them, guess they dissolved in the sauce). 

When the chicken is cold enough, remove all the meat and place it in a bowl. Shred or chop it (with a fork or a hand blender) and return it to the pot. Cook, over medium heat, for 10 minutes (I added 1 cup of water).