Score the skin side of the duck breasts with a knife. Combine the cardamom, coriander, lavender, salt and pepper in a small bowl. Sprinkle the skin side of the duck breasts with the spice mixture. Allow the duck breasts to sit in the refrigerator, uncovered, for 2 days. This will allow the skin to dry slightly, yielding a crispier result. Remove from the refrigerator and let the duck breasts sit at room temperature for 1 hour before cooking.
Place the duck breasts skin-side down in a nonstick pan and begin to cook over a low to medium heat. Let cook, allowing the skin to render its fat and draining it off occasionally, until the skin is fully rendered, brown and crispy, 15 to 20 minutes.
Flip the duck breasts over in the pan, and allow to cook for 3 minutes, basting with fat in the pan. Remove the duck from the pan and allow it to rest for 10 minutes.
Drain some of the excess fat from the pan, then add the shallot. Cook over medium heat until soft, about 2 minutes. Add the cherries, capers and brandy, and flame the pan to cook off the liquid. Reduce to a glaze.
Add the chicken stock and reduce until thick. Season with the red wine vinegar. Slice the duck and serve with the sauce and watercress.