1.5 kgsebago potatoes250 ml (1 cup)milk500 gmbutter, coarsely choppedPinchof finely grated nutmeg, or to taste
Bring potato and a generous amount of cold salted water to the boil in a large saucepan, cook until potatoes are tender (15-20 minutes). Drain in a colander, return to pan to evaporate excess water (5 minutes), pass through a ricer or mouli into a clean pan.
Bring milk to the simmer in a separate saucepan over medium heat, add half to potato and beat to combine. Add butter a little at a time, beating to incorporate well, then beat until glossy. Add enough remaining milk to form a soft purée (you may not need all the milk depending on the amount of starch in the potato), season to taste with nutmeg, freshly ground black pepper and sea salt, and serve hot.