Preparation and cooking time: less than 30 minutes

1. In a small bowl, mix together the sea salt and rosemary Set aside.
2. Pour enough oil into a large saucepan to reach a depth of 2,5 cm / 1 inch. Set the pan over medium heat and heat the oil to 180 °C / 350 °F. Test the oil by dropping in a sliver of sweet potato. It should sizzle immediately.
3. Using a mandoline or a sharp chef's knife, slice the potatoes crosswise into very thin rounds.
4. Carefully drop a handful of potato slices into the hot oil. Use a skimmer or large slotted spoon to turn the potato slices frequently, and fry them for about 2 minutes, or just until they are golden brown. Carefully but quickly remove them from the oil to a large paper-towel-lined rimmed baking sheet.
5. Continue to fry the sweet potatoes in batches until you have fried them all. Let the chips cool to room temperature.
6. Sprinkle some of the rosemary salt over the chips and place the chips in a decorative bowl or napkin-lined basket. Serve the chips at room temperature.
7. Do ahead: The chips may can be fried and salted several hours in advance and kept, uncovered (very important), at room temperature.