Grandma really wasn't a very good cook (some of the stuff she made was pretty scary and is the stuff of family legend) but there were a few things she made really well, including this kugel, which she made only once a year at Passover. She and my grandfather would stand over a tortuous wire mesh grater pulverizing the potatoes by hand. I still have that grater and use it sometimes, or cheat and use the food processor. This is not health food. It is heavy, dense, classic Eastern-European Jewish food, and it is still one of the best things I have ever tasted. —sweetlolo
Preheat oven to 350 degrees. Using a 9 x 12 glass or ceramic baking dish, add enough oil to coat the bottom of the pan with about 1/8 inch of oil. I use safflower oil, but use whatever neutral oil you prefer (not olive oil). Place the pan with the oil in the oven to heat.
Peel the potatoes and onions and grate them very fine, alternating potatoes and onions to keep the potatoes from browning. As mentioned above, my grandmother used a wire mesh grater that she rubbed the potatoes across to pulverize them. You can also use the smallest holes on a box grater, or you can shred them in a food processor, then change to the processing blade and pulse the shredded potatoes in batches, about 5 pulses per batch.
Line a large bowl with a double layer of cheese cloth. Place the grated potatoes and onions in the cheese cloth, gather up the sides and squeeze until you've removed most of the moisture. You want them still to be a little damp, but not dripping with liquid.
Place the squeezed potatoes and onions in a large bowl and mix in the matzoh meal or flour, salt and eggs until well combined. My grandmother used her hands to keep the mixture from getting too compressed, but you can use a spoon or spatula if you are gentle.
Remove the pan with the heated oil from the oven. Moving quickly and carefully, spoon the potato mixture into the pan and smooth it out on top. Some of the oil will rise up the sides of the pan. Spoon some of the oil across the top of the potato mixture.
Place in the oven and bake until dark brown and crispy on top, about 2 to 2 1/2 hours. Be patient, and let it get really dark brown. The darker and crunchier the crust the better it will be.
Remove from oven, cut into 2 inch squares and serve immediately. Leftovers (as if!) can be rewarmed in the oven, and also can be frozen and rewarmed directly from frozen in the oven.