Marinated Chicken Alexandre

Name: Marinated Chicken Alexandre (Marinade de blanc de poularde de Bresse Alexandre)
Yield: For four people
Cuisine: French
Ingredients: 2 large free-range chickens, weighing 2 kg (4½ lb) each; 250 ml (8 fl. oz) chicken demi-glace or well-reduced clarified stock; 250 ml (8 fl. oz) chicken demi-glace or well-reduced clarified stock; 2 tablespoons sherry vinegar; 2 tablespoons wine vinegar; 4 tablespoons olive oil; 2 tablespoons oil of arachide; 1 generous teaspoon strong mustard; 2 cloves; a sprig of thyme; half a bay leaf; ½ teaspoon tarragon, chopped; 1 shallot, finely chopped; a dash of cognac; juice of half a lemon; 100 g (3½ oz) fine French beans, cooked; 1 ripe tomato, peeled, deseeded and cut into quarters; 4 slices of truffle; salt, freshly ground pepper; salt, freshly ground pepper