Finely chop the celery, carrots and onions, fry them gently in a large tall pan in olive oil until softened and golden-brown.
Add the tomatoes, basil, bay leaf, tomato purée, water, salt and freshly ground black pepper.
Mix well, cover with a lid and allow to simmer on a low heat for approximately 30 minutes. (Make sure you stir occasionally). You can blend this sauce with a handheld stick blender (removing the bay leaf first!) or leave it chunky.
This ragu is great for freezing.