Potatoes and sweet leeks simmer in stock, then cream and Swiss or cheddar turn them into a substantial soup. Purée half for a thick base with tender pieces, or make it smooth. A little cheese on top finishes the bowl.
Peel and evenly cut the 2 lb potatoes. Chop the 2 onions and 1 garlic clove. Split the 4 small size leeks, rinse between the layers, and slice.
Melt the 2 tbsp butter in a large, heavy-bottomed saucepan over low heat. Add the potatoes, onions, garlic, and leeks. Sweat for about 10 minutes, stirring often, without browning. (To sweat vegetables, heat fat at medium heat, add vegetables with a sprinkle of salt, and cover with a lid. Do not brown.)
Add the ½ tsp tumeric and enough 4-6 cups chicken or vegetable stock to cover the vegetables. Season (lightly) with ½ tsp each salt and pepper. Bring to a boil, reduce the heat, cover, and simmer until the potatoes are fork-tender, about 15-20 minutes.
Lift out half the vegetables and reserve. Mash or briefly blend the remaining vegetables with the stock, then return the reserved pieces. For a smooth soup, briefly purée all the vegetables instead.
Warm the soup through and adjust the consistency with extra stock if needed. Lower the heat and slowly stir in the 1 cup cream
Take the pan off the heat. Add half the grated 2 cups Swiss or cheddar cheese in small handfuls, stirring until each addition melts.
Add the a dash of nutmeg. and adjust the salt and pepper. Serve in warm bowls with the remaining grated or sliced cheese on top.