Prepare the duck breast: cut off the excess fat, carefully remove the skin and season with salt and pepper. Cook on the skin side in a pan over low heat, until crispy (remove the excess fat from the pan from time to time to avoid burning). Turn on the other side and transfer to a preheated oven for 6-8 minutes at 180°C (355°F).
Peel the boiled potatoes and cut them into cubes. Fry the potatoes in a hot pan with the fat left from frying the duck breast and add salt.
Rinse and clean the spinach. Put a little butter in a hot pan and sauté the spinach. Add the minced garlic, salt, pepper, and flour. Mix for half a minute and then add the milk. Allow to cook for a bit, then blend everything together.
Add the red wine to the same hot pan used to cook the duck breast. Add the berries and reduce the sauce by half. Then add the butter and continue cooking until the sauce starts to thicken.