Cheese and bacon soup

2 tablespoons butter
1/2 leek, the white half
halved lengthwise, washed well and chopped
1 cup sliced mushrooms
1/2 cup cauliflower, chopped
1 1/2 cups chicken stock
2 ounces cheddar cheese, grated
6 strips bacon, cooked and crumble

Heat the butter in a large saucepan over medium heat until the foam subsides. Add the leek, mushrooms and cauliflower. Cover and cook, stirring often for 5 minutes. Add the stock and and bring to the boil. Lower the heat, cover and simmer for 10 minutes. Transfer the mixture to a food proccesor. Add the cheddar cheese and puree for 1 minute, or until smooth. Serve immediately with the crumbed bacon on top.