In a large saucepan, heat the oil until shimmering. Add 4 of the chestnuts and sauté over moderately high heat until lightly browned, about 5 minutes. Transfer to a plate and let cool. Add the onion and leek to the pan, cover and cook over moderate heat, stirring occasionally, until softened, about 5 minutes. Uncover and cook over moderately high heat, stirring frequently, until lightly browned, about 4 minutes. Add the honey and stir until melted. Stir in the remaining chestnuts and the stock, season with salt and pepper and simmer over moderate heat for 10 minutes.