First you have to prepare the sauce. In a frying pan, fry the onion that will have been finely grated. Once the onion begins to brown, pour in the wine. Cook for 10 minutes to evaporate and immediately add the cream. Towards the end, add the berries, so they don't fall apart too much. Reserve the sauce to put it on top of the meat when it is done.
Salt and pepper the duck magret, putting them in a Tefal frying pan. Put a little oil, and when it is hot, you will put the magret on the fat side for 6 minutes. Go throwing the oil that will be leaving over the magret, so that it does not get too sticky. When the 6 minutes are up, turn the pieces for 4 more minutes. We take them out and cut them a little thin. Distribute the meat on plates, and pour the sauce that we will have prepared on top.