Wash the potatoes and cook them in salted water.
Meanwhile, clean the leek by removing the green part. Wash it and slice it.
In a non-stick pan, cook the leek with a little oil until soft, adding a little water as needed. Puree with a mixer.
Heat the milk with nutmeg.
Once the potatoes are cooked, peel them and press them with the potato ricer. Add the leek puree, 50 gr. of butter and mix everything adding the milk a little at a time until you get a creamy consistency. Season with salt.
In a small saucepan, brown the remaining butter with the fresh sage.
Wash and cut the chives into small pieces.
Add the browned butter, the chives and complete with a few walnut kernels.
Serve hot