Preheat the oven to 200'C.
Trim the excess fat and sinew from the duck breasts. Score a criss-cross pattern into the fat without cutting into the flesh.
Heat a frying pan to a medium heat and add the duck breast straight to the pan without any oil. Cook for about 3 minutes until the fat has melted and the meat starts to colour. Season with salt and then transfer a baking sheet and cook in the oven for 6 minutes. Allow to rest before carving.
Add the red wine, sugar and raspberries to the pan used to cook the duck. Reduce by two thirds.
Peel and wash the potatoes and then grate on the largest side of a vegetable grater. Peel the onion and slice thinly. Coarsely chop the tarragon. Combine these ingredients season generously. Take handfuls of the mixture and press into flat rounds.
Heat a frying pan and add olive oil. Cook the rosti for 5 minutes on each side. They should be crisp and golden brown.
Cut the duck breasts into slices and serve alongside a rosti and the raspberry and red wine sauce.
«Cook the sauce over a high heat to ensure it reduces quickly and can be served while the duck is hot.»