In a large stock pot, melt the butter with olive oil, over medium heat. Put the onion and leeks in the stock pot and sauté for a few minutes. Then add the carrots, turnip, squash, and sauté an additionnal 10 minutes over medium heat, stirring regularly. Add the garlic, cumin, chili powder and salt & pepper to taste. Mix well. Add the stock plus enough water to cover the vegetables so they swim in the liquids. Add the rice. Lower the heat to simmer and cook, covered for 40 minutes or more.

Remove from heat and purée the soup using a hand-held processor or food processor. Soup will be thick. Add milk and additional water to desired consistancy. Stir to mix well. Reheat to simmer. Add chopped coriander before serving.