Turn the oven on and set the heat to 425 degrees. Lightly oil the baking sheet (or sheets) by spreading the oil around with your clean hand or a paper towel.
Put the flour, baking powder, and salt in the small bowl and mix well.
Use the large holes on your grater to grate the potatoes and onion onto the plate.
Put the colander in the sink and put the potato and onion mixture into it. Using a paper towel, press the potato mixture down to squeeze out and blot up some of the extra liquid. Stir the mixture and press and blot again.
Put the potato mixture in the large bowl, add the egg, and stir well. Add the flour mixture and stir in very well.
Pick up a clump of the potato mixture using a spoon or your clean fingers. 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 much space between them.)
Once the oven temperature has reached 425 degrees, carefully put the baking sheet in the oven and bake until the bottoms are deeply golden, 15-20 minutes.
Turn the latkes over and bake until they are very crispy, 10-15 minutes. Serve right away with applesauce and yogurt.