Soups - Sweet Potato and Leek Soup with Bacon and Chives

8 medium leeks, white parts only
12 strips double-smoked country bacon
6 T unsalted butter
2 med sweet potatoes, peeled and thinly sliced
6 cups chicken stock
Salt and freshly ground black pepper
3 T snipped fresh chives

Wash the leeks carefully to remove all grit, then thinly slice them. Fry the bacon over medium heat. As it cooks, drain off and reserve the fat, and remove the strips to a plate lined with paper towels. Set aside. Wipe the pan clean, add 2 T reserved bacon drippings along with butter. Over low heat, sweat the leeks, stirring occasionally until they are very soft, about 25 mins. Add sweet potatoes and stock, cover and bring to a boil. Reduce the heat and simmer, uncovered, until potatoes are very soft, about 35 mins. Transfer soup in batches to a blender or food processor and puree until smooth. Season with s & p to taste, stir in chives. To serve, ladle soup into bowls and top with crumbled bacon. Serves 4-6.