Season the pieces of chicken on both sides with salt and freshly ground pepper. Heat the butter and olive oil in a large sauté pan. Brown the pieces of chicken over a medium heat, turning them over from time to time. When they are golden all over add the tomatoes and let their juices evaporate, continuing to turn the pieces of chicken from time to time. When the tomatoes have turned into a thickish sauce, add the garlic, anchovies and vinegar. Stir them together with the tomatoes and chicken, adding lemon juice and stock cube and sugar. Season and continue to cook, turning the chicken pieces occasionally, until the juices and liquids have reduced once more to a rich consistency.
Serve with French beans cooked with garlic.