Season flanken with salt.

Heat a large soup pot over high flame. Add oil and sear meat on all sides, working in batches so as not to overcrowd the pot. Remove the meat from the pot and set aside.

Add all vegetables to the pot and cover. Let the vegetables sweat until onions are translucent, about 10 minutes.

Return meat to the pot and cover with stock and/or water. Season with salt and pepper. Cover and bring to a boil, then lower heat to a simmer until meat is extremely tender, about two to three hours.

Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius).

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.

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.

When ready to serve, add several gnocchi to each bowl and ladle soup over them.