Score the skin of the duck breasts. Heat a heavy-bottomed frying pan. Cook the duck breasts on medium heat, skin side first.
After 8 min, turn them over without piercing them and cook for another 6 minute Season with salt and pepper. Keep the breasts warm on a plate, covered with aluminium foil.
Discard the cooking fat and in the same frying pan, bring the sherry vinegar to the boil and reduce for 1 min on a high heat. Add the Cherry brandy and the Griottines, cook for about 5 min on low heat, shaking the pan from time to time to move the fruit without damaging them.
Return the duck breasts to the pan, with the cooking juices from the plate. Reheat them with the cherries for 2 to 3 minute.
Cut the breasts into slices. Arrange them on warm plates, sprinkle with chopped tarragon, add the Griottines and serve immediately with a small herb salad garnished with croutons and lardons.