In large casserole dish over a high heat, brown the chicken on all sides. Remove and set aside.
Turn down the heat to medium and add olive oil. Cook and stir onion and garlic for 2 to 3 minutes until soft. Add celery and leek and cook and stir until both are soft. Add tomatoes and stock and simmer over low heat for 15 minutes.
Remove from the stove, let cool and then purée in a blender or with a handheld mixer. If you want the sauce to be especially smooth, you can also strain it through a fine sieve.
Pour sauce back into the casserole dish, season with salt and pepper to taste and add carrot and chicken. Cover.
Stew in the preheated oven for about 50 minutes, until the chicken juices run clear. Remove the lid to brown the chicken skin 10 to 15 minutes before the chicken is done.
To serve, sprinkle with fresh parsley.
Instead of two chicken legs, you can use a variety of chicken parts, or four bone-in thighs.