Grate potatoes and onion into a large bowl. Add some water just to cover the potatoes so that they don't brown while you are grating the rest. Let stand for 10 minutes to let the liquid from the potatoes and onion separate and rise to the top. Remove the liquid and then pat the potatoes and onions dry to remove any excess water. This helps them crisp up in the pan.
Stir in the eggs, salt, pepper and baking powder. Add the flour to thicken the mixture up and bind the eggs and potatoes together. The mixture will still be thin.
Heat the vegetable oil in a pan over medium-high heat. Oil in the pan should be about 1/4" deep. I like to test by putting a small pinch of flour in the pan when I think it is hot enough. If it sizzles the oil is ready to go.
Drop heaping tablespoons full of the potato mixture into the heated oil and using a spoon coax it to form a small 3" circle. Fry until the bottom is brown before flipping otherwise the bottom will stick and it won't flip well. Once the bottom is brown gently flip the potato patty and continue to fry until the other side is golden brown.
Remove from the pan when done and place on paper towels to drain. Continue until all the batter is used. Serve hot with sour cream, apple sauce or powdered sugar.
Notes
Store in a tightly sealed container in the fridge for up to 3 days. Reheating in the oven or air fryer is best to crisp them up again but you can also microwave them as well.