How to Make It
In a large saucepan, heat the oil. Add the bacon and cook over moderate heat, stirring occasionally, until crisp, about 8 minutes. Using a slotted spoon, transfer to a paper towel–lined plate to drain. Add the leek, celery, carrot, garlic and ginger to the saucepan and season with salt and pepper. Cook over moderate heat, stirring occasionally, until the vegetables are beginning to soften, about 8 minutes. Stir in the cumin and cook until fragrant, 30 seconds. Add the stock, cider and lentils and simmer, stirring occasionally, until the lentils are tender, about 40 minutes. Stir in the apple and rosemary and cook until the apple is just softened, about 3 minutes. Season with salt and pepper and ladle into bowls. Drizzle the soup with buttermilk, garnish with the bacon and serve.