1. Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius).
2. Bake potatoes until fully cooked and tender all the way through, about one hour. Mash the potatoes well using a potato ricer or by pushing the potatoes through a colander or sieve with a spoon. Add yolks, flour, and salt and mix carefully and lightly, trying not to press down too hard on the potatoes. It should form a cohesive dough.
3. Roll the dough into logs on a surface liberally sprinkled with Pesach flour, applying light pressure. Cut into one-inch (two-and-a-half-centimeter) sections and toss with a bit more Pesach flour. Drop into very well-salted boiling water in batches, removing them as soon as they float to the surface.
4. When ready to serve, add several gnocchi to each bowl and ladle soup over them.