Preheat the oven to 1 90°C

Bring a saucepan of lightly salted water to the boil, cut the parsnips, potatoes, carrots and sweet potatoes into chunks and add them to the pan

Bring the water back to the boil and cook for about 2 minutes then drain the vegetables thoroughly

Pour the olive oil into a large heavy roasting tin and place over a moderate heat, add the vegetables, shallots and garlic, fry tossing the vegetables over the heat until they are pale golden at the edges

Add the mustard seeds, coriander seeds, cumin seeds and bay leaves, then cook for 1 minute, then season with salt and pepper to taste

Transfer the roasting tin to the oven and roast for about 45 minutes turning occasionally until the vegetables are crisp and golden and cooked through