Put 2 level tablespoons of potted duck fat into a saucepan with the onions and fry. As soon as they start to brown, put in the green peas, stir for a few minutes. When hot, dust with flour, salt, papper, add a sugar lump and the bouquet garni, moisten with 4 tablespoons of water, cover. Cook over a low heat until the peas almost melt. Meanwhile, trim the fat off the duck and brown, placed on the rack of the dripping-pan. To serve, add to the peas the juice of the potted duck (aspic or liquid) if you had bought it canned. Otherwise, add a tablespoon of the grease collected in the dripping-pan. Serve the green peas topped with the duck cut into pieces.