Cook 4 bacon slices in a skillet until crisp. Remove, leaving the drippings in the pan. Melt 2 tablespoons butter with the drippings over medium heat. Add 1 chopped leek and 1 chopped peeled russet potato. Cook until the leek is softened, about 5 minutes. Add 2 cups chicken broth and 1 cup heavy cream. Simmer until the potatoes are tender, about 15 minutes, then puree in a blender in batches until smooth. Serve in small glasses; chop the bacon and sprinkle on top.