For the mashed potatoes, peel, wash and dice the potatoes. Cook in a pot of salted water, barely covered, until soft. Strain, set aside some of the cooking water.
Using a potato masher, mash the potatoes, add butter and milk, mash everything well. Then mix with a whisk, if too firm add some of the cooking water, season with salt and nutmeg.
Arrange on plates, drizzle with the pumpkin seed oil (more or less according to taste).