Preheat oven to 375°. Peel potatoes and cut into 1/8-in. slices.
Heat 2 teaspoons oil in a 10-in. ovenproof nonstick frying pan over medium-high heat. Arrange about one-fifth of the potatoes in a circular pattern in the pan.
Potatoes should sizzle when you put them down; if they don't, wait for the pan to get hot enough.
Mix salt and rosemary in a bowl. Sprinkle potatoes with about one-fifth of the rosemary salt.
When potatoes begin to brown around the edges, reduce heat to low.
Repeat layering 4 times, sprinkling with a little of the rosemary salt each time (brush final layer with remaining 1 teaspoons oil before sprinkling with last of salt).
With a heatproof spatula, gently pull back potatoes to see if the bottom layer is starting to brown. If it is, transfer pan to oven and bake until potatoes are tender when pierced with a fork, 45 minutes.
If it isn't, increase heat to medium-high and cook until bottom layer is browning before transferring to oven. If potatoes start to look dry or curl up, cover with foil.
Run spatula between potatoes and pan sides and invert potatoes onto a plate or flat platter. Serve hot or warm, cut into 8 wedges with a serrated knife.