Duck Breast: Score the duck breast fat in a criss cross fashion. Place the duck breast in a container with the garlic, orange zest and thyme. Cover the container and place it in a refrigerator, leave it to infuse for 1-3 hours.
To Cook: Place a large frying pan over a moderate-high heat. Season the duck breast with salt and pepper, being sure to rub plenty of salt into the scored fat. Place the duck breast in the hot frying pan fat side down. Cook the breast for 3-4 minutes on the skin side, then turn them over and cook them for a further 4-5 minutes (a little longer if you like the meat well cooked). Remove the duck breast from the heat and allow them to rest in a warm place for 3-5 minutes before serving.
Blueberry Port Sauce: Place half the blueberries in a saucepan with the port and redcurrant jelly. Place the pan over a high heat and leave to simmer for 8-10 minutes until it reduces to a thin sauce consistency. Remove the pan from the heat and stir in the Dijon mustard and the remaining blueberries. Keep the sauce hot until ready to serve.
Spinach: Place the olive oil in a large saucepan and place it over a moderate-high heat. Add the spinach to the pan and sauté it for 3-5 minutes stirring it regularly until it has reduced right down into tender leaves, stir in the nutmeg and seasoning. Serve or keep warm until ready to serve.
To Serve: Place the duck breast on serving plates, pour the blueberry and port sauce around the breast. Place a rosti beside the duck accompanied by a generous serving of spinach.