Peel and chop onion, squash and carrot into large chunks and place on a roasting tray. Sprinkle with oil, cumin seeds, salt and pepper and put in the oven for 20 - 30 minutes. The vegetables should be soft but not mushy and slightly caramelised.
In a large saucepan place the stock, bay leaves and roasted vegetables. Bring to the boil and simmer for a further 20 mins. When the vegetables are soft remove the bay leaves and any outer onion leaves which look fibrous then blend soup until smooth.
Adjust seasoning to taste and serve with a dollop of soured cream and some crusty bread.