Place the potatoes in a medium size sauce pot and cover with cold water. Make sure the water is about 1 inch over the potatoes. Bring up to a boil on medium heat and cook until tender.
Drain and set aside.
Once the potatoes are cool enough to handle, gently smash them with the flat side of a large knife. You want them to flatten but not fall apart.
Bring a medium size cast iron skillet up to heat over medium high. Add in the grapeseed oil. Working in batches add the smashed potatoes. Once they crisp up on one side, flip and crisp the other. Push them to one side of the pan to add more potatoes.
Once they have all crisped up stir them around the pan, this will start to break them up and get the little bits even crispier. Season liberally with truffle salt and pepper. Add in the fresh rosemary. You want the rosemary to cook slightly but not burn and turn black.
Taste for seasoning, adding more truffle salt if needed. Serve immediately.