Grate the potatoes and onion in a food processor with the grating disk. Squeeze on some lemon juice to prevent the potatoes from browning. Dump into a bowl. Place the metal blade in the processor and return the potatoes to the processor bowl. Pulse a few times to make a finer texture. Drain off fluid.
Add the remaining ingredients to the potatoes and pulse a few times to blend. Let stand 15 minutes so that the matzo meal can soften.
Place about 1/2" of oil in a large, heavy skillet or electric skillet. Heat
to about 400° F., just under the smoking point. Use a serving or other
large spoon to spoon potato batter into the hot oil. Flatten lightly. The
latkes should be about 3-4" long and about 1/2" thick. Cook until well
browned. Turn and cook the other side. It will be necessary to raise and
lower the heat depending upon how fast the latkes are cooking. The hotter
the oil the less greasy the pancakes will be. Drain the pancakes on paper
towels and set in the oven on low until all of the pancakes have been cooked.
If you like very crispy pancakes, slide the cooked pancakes back into very
hot oil, just before serving to restore crispness ( drain again before
serving). We do this in at least two pans so that they will get done faster
and will therefore be crisper when eaten.