Peel the potatoes and boil in lightly salted water. Let them cool a little and then put through a potato ricer while still warm. On a work surface, combine the potatoes with the butter, flour, cornstarch, cottage cheese, egg, egg yolk, semolina, salt and nutmeg, and work into a smooth, elastic dough. Form a 3 cm thick roll, and using a cutter, cut out pieces about a thumb thickness wide. On a floured surface, make small noodles out of the dough.
Place on a baking tray sprinkled with semolina. Line a large cooking pot with baking paper and leave some paper for covering. Fill the pot with water, bring to boil and put the noodles in. Cover the water with baking paper and simmer, lightly bubbling, for about 5 minutes. (This way, the noodles stay under water and won’t stick together). Remove with a draining spoon and let drain. For the poppy seed crumbs, froth up the butter and combine with the rest of the ingredients. Toss the noodles well in the mixture. Serve on warmed plates and sprinkle with icing sugar.