(or larger pottatoes cut in half)
Boil the potatoes:Put the potatoes in a large saucepan (preferably in one layer) and cover with at least an inch of water. Add 2 tsp. kosher salt to the water. Bring the water to a boil over high heat, reduce to a simmer, and cook the potatoes until they are completely tender and can be easily pierced with a metal or wood skewer. Make sure they are cooked through but don’t overcook. The total cooking time will be 30 to 35 minutes.
While the potatoes are cooking, set up a double layer of clean dishtowels on your countertop. As the potatoes finish cooking, remove them individually from the water, and let them drain and sit for just a minute or two on the dishtowels.
Flatten and cool the potatoes:Fold another dishtowel into quarters, and using it as a cover, gently press down on one potato with the palm of your hand to flatten it to a thickness of about 1/2 inch. Repeat with all the potatoes. Don’t worry if some break apart a bit; you can still use them.
Cover a large rimmed baking sheet with aluminum foil; put a sheet of parchment on top of the foil. Transfer the flattened potatoes carefully to the baking sheet and let them cool completely at room temperature.