Grate the peeled potatoes and onion on the coarse side of a box grater onto a baking tray. Scoop them onto the middle of a clean tea towel and gather the cloth around the mixture into a pouch. Holding the pouch over the sink, twist the cloth tightly to squeeze out as much liquid as you can. Unravel the pouch, loosen the mixture and give it another good squeeze.
Lightly beat the eggs in a large mixing bowl, add the matzo meal and baking powder and season generously with salt and pepper. Whisk until smooth.
Add the grated and squeezed potato and onion to the bowl and mix well.
You will need to cook the latkes in batches. Heat half the sunflower oil in a large frying pan over a medium heat. Using two dessertspoons, scoop mounds of the potato mixture into the pan and flatten slightly. Cook the latkes until golden-brown and crisp on one side and then using a fish slice flip over and cook the other side until golden-brown.
Remove the latkes from the pan and place on a baking tray lined with kitchen paper to absorb any excess oil. Cook the remaining latkes in batches, adding more oil to the pan as needed.
Latkes can be prepared ahead of time and reheated in a preheated 180C/160C Fan/Gas 4 oven for 10 minutes, or until hot through.