Peel and grate the potatoes (I prefer about 2/3 fine and 1/3 shredded). Potatoes will turn brown if they sit in their own liquid for any length of time. If possible, grate them in a strainer or onto cheesecloth in a glass bowl to allow the liquid to fall through. Otherwise, adding a tiny bit of lemon juice or cream of tartar slows browning. Anyhow, remove as much liquid as possible from the potatoes.
Start heating the oil over high heat (if you have a vent fan, you'll want to use it). By the time the latkes are ready to fry, the oil must be very hot, but not smoking.
Grate the onions on the fine side of the grater (same as used for the potatoes) into the potatoes.
Add the eggs, matzo meal and baking powder, and mix with a spoon til blended.
Gently spoon onto the griddle; flatten slightly with the back of the spoon to keep them an even height. (Your choice of size, but I suggest small-to medium). Fry until nicely browned and crisp at the edges; turn carefully with a spatula and spoon (hot oil will spatter and burn if you simply flip them). When done, place on the prepared platter.
Serve immediately with applesauce and sour cream. Salt to taste.