First clean the celery, carrot, onion and chop them. Then fry the vegetables with 1 tablespoon of oil in a saucepan or directly in the crock pot - which you will put on the stove after removing it from the outer container.
Finally add the chicken and brown the skin.
At this point remove the container from the stove and put it in the Cooker pot, or if you had cooked everything in a saucepan, transfer allthe ingredients to the crock pot.
Take half of the vegetables and create a layer at the base of the pan on which you will arrange the chicken pieces.
Add the sprig of rosemary, garlic cut in half and the chopped parsley.
Finally the tomatoes and the remaining part of the vegetables set aside previously so that the chicken is covered both above and below by the vegetables.
Finish with salt, pepper, and 2 tablespoons of extra virginolive oil.
Place the lid on, and cook for 3 hours and 30 minutes at the maximum temperature (HIGH) or 7 - 8 hours on the low temperature (LOW).
Once cooked, if you want a creamier sauce you can blend apart of it with a blender.
Your chicken and vegetables are ready to be served!