How to Make It
In a large saucepan, combine the wine, sugar and bay leaf and bring to a boil, stirring to dissolve the sugar. Boil until syrupy, about 9 minutes. Add the cranberries and cook until they begin to break down, about 5 minutes. In a small bowl, whisk the vinegar with the mustard, then whisk the mixture into the cranberries. Season with salt and pepper.
Meanwhile, heat a large, heavy skillet until very hot. Lightly rub the duck skin with vegetable oil and add the breasts to the skillet, skin side down. Cook over moderately low heat until the skin is golden and crisp, about 15 minutes. As the fat renders, spoon it into a heatproof bowl. Season the duck breasts with salt and pepper, turn them and cook over moderately low heat until browned on the bottom, about 8 minutes. Transfer the duck to a plate and keep warm.
Add 2 tablespoons of the reserved duck fat to the skillet and heat until shimmering. Add the quartered endives, season with salt and pepper and cook over moderately high heat, turning occasionally, until softened and golden, about 6 minutes. Slice the duck breasts and transfer to plates. Serve the duck with the quartered endives and cranberry mostaza.