Peel the potatoes and grate them coarsely into a large bowl of cold water. The water keeps the shreds from browning while you work.

Grate the onion, if using, directly into the same bowl.

Let the mixture sit undisturbed for 10 minutes. The potato starch will sink and settle as a chalky white layer at the bottom of the bowl.

Carefully pour off the cloudy water on top without disturbing the settled starch, then tip the grated potato into a strainer set over the same bowl and press out as much remaining liquid as you can.

Pour off the water from the bowl a second time, leaving just the thick white starch paste stuck to the bottom.

Scrape that settled starch into the drained potato shreds along with the salt, and mix by hand until it binds into a loose, sticky mass. No flour needed.

Heat 2 tablespoons of oil in a nonstick pan over medium heat until shimmering.

Spread a portion of the potato mixture into a thin, even round, about 5 mm / 1/4 in thick, pressing it flat with the back of a spoon.

Cook undisturbed for 5 to 6 minutes, until the underside is deep golden and firm enough to slide a spatula fully under it without tearing.

Flip and cook the second side 4 to 5 minutes, pressing down once to flatten it evenly against the pan.

Repeat with the remaining mixture, adding oil to the pan between batches. Serve hot with the dipping sauce.