In a medium soup pot, heat the oil until hot. Add the bacon, onion, jalapeños and garlic and cook over moderately high heat until the onion is softened and the bacon fat has been rendered, about 5 minutes. Add the chili powder and cook over moderate heat until fragrant, about 1 minute. Stir in the beans, tomatoes and stock and bring to a simmer. Simmer the chili over moderately low heat until thickened, about 15 minutes. Season with salt and pepper and serve with cilantro and sour cream.