These instructions assume you’re using a food processor.
Cut the potatoes into chunks that will work with your food processor. You don’t have to peel the potatoes, just scrub them well and go over them with a knife to remove anything undesirable.
In the food processor: grate the potatoes with the fine-grating disk.
Dump the grated mass into a colander and rinse briefly to avoid discoloration. Allow to drain while everything else is being prepared.
Rinse the food processor; fit the knife in.
Peel and quarter the 3 onions; purée them in the food processor.
Add the eggs to the puréed onions; blend them for a few seconds.
Add the 1 1/2 teaspoon of salt, the pepper, flour, and baking powder to the contents of the food processor. Whirl until all is smooth.
Put the grated potatoes in a big bowl and mix the batter into that.
Pour another tablespoon of oil into the pan and heat it. Using a quarter of a measuring cup, turn out little hills of raw batter into the hot oil. This works better than using cooking spoons. Flatten out the tops a little. Fry until the first side is brown; gently flip over with a spatula and fry until the other side is brown, too. Taste the first one or two to determine what color the pancakes have to be when they’re done. The oil in the pan will need to be renewed once in a while.