Wash hands with soap and water.

Preheat the oven to 425 °F. Lightly oil the baking sheets by spreading the oil around with your clean hand or a paper towel.

Mix the flour, baking powder, and salt in a small bowl.

Use the large holes on your grater to grate the potato, then grate the onion too.

Put the potato and onion mixture in the colander inside the sink. Using a paper towel, press the potato mixture down to squeeze out and blot up some of the extra moisture. Stir it and blot again.

Put the potato mixture in the large bowl, add the egg, and stir well. Add the flour mixture and stir it very well.

Use a spoon or your fingers to pluck a clump of the potato mixture from the bowl and spread it into a round, flat nest on the oiled baking sheet: it should make a circle that's about 3 inches wide and 1/4 inch thick. Repeat to fill the sheet. (You don't need to leave space between them.)

Bake until the bottoms are deeply golden, 15 to 20 minutes, then turn the pancakes over and put them back in the over for 10 more minutes.