In a large pot or dutch oven, heat the olive oil over medium heat and add the onion, garlic, celery and carrot. Saute for about 10-15 minutes, turning heat down if it's too much. You want a fair bit of colour and caramelisation over the veggies, as this is what is going to provide the flavour. I often cook mine for 20 minutes or more.
When you're happy with the colour on the veggies, add the turnip and canned tomatoes, the water, basil, oregano, bay leaf and pinch of sugar.
Bring to a boil, then return to a simmer for as long as you've got. Pop in your piece of parmesan-style cheese rind and let it do its thing. I simmer mine over low heat for about three hours, topping up with water as necessary to the level I wanted - I don't mind a bit of broth as opposed to veggies, but you keep an eye on it to keep it at the ratio you want.
For the last hour, add the rinsed and drained cannellini and taste for seasoning.
This soup only gets better so feel free to make it the day before you need it, or enjoy for leftovers! Serve with a drizzle of olive oil and a sprinkle of salt.