Peel the potatoes and shred them with the large holes of a box grater. Finely chop the onion so it blends into the mixture. I work fast here because shredded potatoes can turn gray if they sit too long.
Place the shredded potatoes in a clean kitchen towel and twist it over the sink. Squeeze hard until very little liquid drips out. I do this in two batches, because a drier mixture gives me a much crispier pancake.
Move the drained potatoes to a large bowl and add the eggs, flour, baking powder, salt, and pepper. Stir in the chopped onion until everything looks evenly coated. The mixture should hold together loosely when you press it.
Pour the oil into a large skillet and set it over medium-high heat. Wait until the oil shimmers and a shred of potato sizzles right away. If the oil is not hot enough, the pancakes will turn greasy and soggy.
Scoop a heaping spoonful of batter into the pan and flatten it gently into a round. Leave a little space between each pancake so they brown well. Cook them for about four to five minutes until the bottoms are deep golden.
Turn each pancake carefully with a spatula and press it down lightly. Fry the second side for another three to four minutes until crisp all over. I like to peek underneath before flipping, so I never pull them too early.
Move the cooked pancakes to a wire rack or a plate lined with paper towels. Sprinkle a tiny pinch of salt on top while they are still hot. Serve them right away, because they taste best when they are warm and crunchy.