Peel the potatoes and dice them, put them to boil (check to see if they're ready from time to time with a fork).
While they're cooking, finely chop the onion head, cheese and parsley. Get your "breadcrumbs" ready too - crumble the rusks in a bowl, mortar and pestle or use a hand blender. Be careful not too crumble them too finely - the idea is to have larger pieces that crunch.
Once the potatoes are ready, drain out the water and put them in cold water briefly to cool (or just wait for awhile). Pour them into a bowl, mash them a little with a fork (be careful not to mash them to a paste, you need to still have pieces).
Next, in order to work fast, make an "assembly line", so to speak, on the counter in the following order: a bowl of cool-warm water, the potato mixture bowl next to it, then a deep plate with the crumbled rusks and finally a flat oven dish laid out with baking paper.
Make the meatballs as follows: dip your hands in the water, shape flat meatballs, roll them well in the prepared rusks (they're going to stick to the wet surface) and place in the oven dish. Continue until you've used up all of the mixture.
Place the prepared meatballs in the preheated oven for about 15 min. Then, using a spatula or tongs, flip them over and bake for another 10-15 min. Serve them warm with a dairy sauce or garnish of your choice (salad, for example).