Heat the oven to 450 degrees.
In a large dutch oven, add chicken, carrots, celery, garlic, leeks, onions and tomatoes. Evenly distribute the oil over the chicken and vegetables.
Place the dutch oven into the oven and cook for 30 minutes.
Meanwhile, bundle the bay leaves, parsley stems and thyme and tie with kitchen twine.
Remove the dutch oven from the oven and place on the stove-top. Add water, herbs and peppercorns to the dutch oven. Bring to a boil.
Reduce to a moderate simmer and let cook for 2 ½ hours or until the liquid is reduced by half.
Remove the dutch oven from the stove-top. Remove the chicken to a cutting board and let cool. Strain the stock from the vegetables and let cool. Store in an airtight container in the fridge or freeze after cooling completely.