Slice the potatoes very thinly in a food processor or
with a mandoline. Place in a bowl of cold water and
rinse
well. Drain well and dry on kitchen
paper.
Pour
half the butter into a flat-bottomed wok or frying pan.
Arrange the potato slices in the pan, overlapping
slightly like the scales of a fish. Spoon over some more
butter.
Continue layering the potato slices in the pan,
finishing with butter. Cook for
about 2 minutes, shaking the pan with a circular
movement to prevent the potatoes from sticking.
Press
down the galette with the back of a spoon and cook for
10 minutes.
Turn over with a spatula and cook the other
side for 10 minutes. Drain
off the butter, tilting the pan but keeping the galette
in position.
Slide onto a warmed serving plate, garnish
with parsley or coriander, and serve immediately.