Put the potatoes in a large saucepan or Dutch oven (preferably in one layer) and cover with at least 1 inch of water. Add 2 teaspoons of Kosher salt to the water. Bring the water to a boil over high heat, reduce heat to a good simmer, and cook the potatoes until they are completely tender and can be easily pierced with a metal or wooden 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.
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 ½ 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 paper on top of the foil. Transfer the flatten potatoes carefully to the baking sheet and let them cool completely at room temperature.
If making ahead, cover loosely with plastic wrap and refrigerate. Otherwise, continue on with roasting directions.
Remove the pan of potatoes from the refrigerator, if prepared ahead. Heat oven to 450 degrees. Alternatively, if you have a convection function, turn it on and set the temperature at 400 degrees. Sprinkle the potatoes with about ¾ teaspoon of salt and pour the olive oil over them. Lift the potatoes gently to make sure some of the oil goes underneath them and they are well coated on both sides. Roast the potatoes until they are crispy and deep brown around the edges, about 30 minutes if using convection, 30 to 40 minutes if roasting conventionally, turning over once gently with a spatula or tongs half way through cooking. Serve hot.
*Make Ahead Tip: Do the busy work-boiling and flattening the potatoes-up to 8 hours ahead. Let the potatoes cool completely, and store them on the pan, lightly covered in the fridge. Then all you have to do at the last minute is coat with oil and salt and roast.