Peel the potatoes and grate them on a fine grater directly into a large, flat bowl. Leave them in the bowl without stirring, tilt the bowl gently, and set aside for about 5 minutes.
In the meantime, pour off the accumulated juice, gently holding the potatoes, still without stirring them. At the end, press down with your hand against the bowl and pour off even more juice. Add the flour, finely grated onion, egg, and two pinches of salt.
Heat the pan and pour in the oil. Mix the potato mixture. Place portions of the mixture (1 heaping tablespoon) onto the heated oil and spread it into a fairly thin pancake. Fry over medium heat for about 2-3 minutes until golden, then flip to the other side and repeat frying.
Place on a plate lined with paper towels. Sprinkle with sea salt from a grinder. Potato pancakes are best straight from the pan when they are crispy.