Pour a layer of salt about 2 cm thick into a vessel with a lid (earthenware terrine, for example) that is slightly larger than the duck fillet. Place the duck fillet on top and cover completely with salt (you can press the salt on a little and add herbs such as thyme to taste). Let the whole thing dry in the fridge for at least 24 hours (30 hours is better).
Then take the duck fillet out of the salt, clean it well (you can also rinse it briefly under water and dry it well with kitchen paper).
Place on a clean kitchen towel and pepper well on all sides. Wrap in the cloth and let it dry for 2 to 3 weeks. This is best done in an airy basement or in the pantry - if this is not feasible, then it is downstairs in the refrigerator.
To serve, cut into wafer-thin slices and serve as a starter, e.g. with fresh bread and butter. Also goes very well with a green salad.
A strong red wine (e.g. Cahors) goes best with it.