Grate the potatoes: Grate half of the potatoes and the onion on the big holes of a box grater, then grate the remaining potatoes on the small holes of a box grater. Mix together with 1 teaspoon of salt and let stand for 15 minutes.
Drain the potatoes: After this time squeeze out as much water as you can from the potatoes, reserving the water in another bowl (!) (I'm just taking a handful of grated potatoes and squeeze them out with my hands, but you can also use a fine mesh-strained and a spoon or wrap the potatoes in a clean kitchen cloth to do it). Discard the liquid from the bowl, leaving a thick white paste that will be at the bottom of the bowl (potato starch).
Combine with the other ingredients: Combine the grated and drained potatoes and onion with a lightly beaten egg, and potato starch together. Season lightly with salt (the mixture should be at this point lightly salty) and generously with black pepper.
Fry: Pour a couple of tablespoons of frying oil into the pan and warm it up over medium or medium-high heat (the amount of oil will depend on how big the pan is, there should be enough oil to cover a minimum of 1/3 of the thickness of the pancakes, and better would be at least 1/2 of their thickness). When the oil is hot, scoop 3-4 heaped tablespoons of batter onto the pan (or as many as will fit in your pan without overcrowding the pancakes, about 1 heaped tablespoon of batter per pancake), flatten it with a fork into rounds about 1/4 - 1/3 inch (1/2 - 3/4 cm) thick. Cook until golden then flip over and cook on the other side until golden. Transfer to a plate lined with paper towels to drain the excess fat.
Enjoy!