Heat the olive oil in a large casserole pot over a medium heat and add the onions, garlic, carrots, fennel, parsnips and leeks, stirring occasionally until they soften.
Add the curry powder, herbs de provence, ginger purée, turnip and sweet potato, cover and reduce the heat, stirring occasionally for roughly 15 mins until the hard vegetables have softened slightly.
Prepare the vegetable stock, (I use two stock cubes as they really thicken the stock and add much more depth of flavour) and transfer the cooked vegetables to a slow cooker. Pour the stock over the vegetables and add the passata and tomato purée. Stir everything together, add the rosemary and bay leaf and season with salt and pepper to taste. Leave this to cook in the slow cooker on high for 2 hours, stirring every 30-45 mins.
Prepare your mushrooms – wash and quarter them, removing the lower portion of the stalks – and add stir them into the slow cooker along with the finely chopped basil leaves. Taste and adjust seasoning as necessary – you can also remove the rosemary and bay leaf at this point if you wish.
Leave the stew in the slow cooker on low for another 3+ hours, the longer the better really. I leave mine for approximately 4½ hours, allow it to cool and heat it up the following day for eating. Leaving it to rest overnight allows the flavours to develop further, but this isn’t really necessary.
If you don’t have a slow cooker, simply add the stock, passata and tomato purée directly to the casserole dish along with the bay leaf and rosemary and leave it on a low heat for 2 hours. Then add in the mushrooms and basil before transferring to a medium/low oven for 3+ hours.
This recipe really goes well with herby dumplings or good crusty bread.