Heat a small non stick pan over medium-high heat. Add the oil (a bit more than you would think...about 1/8 of an inch).
When you think the oil is hot, test it by dropping in a potato shred—it should sizzle. If not, wait a few more seconds.
When the temperature is right, put a hand full of potatoes in the center of the pan. (Be careful because the oil will spatter)
Adjust the heat so that you hear a sizzle but the bottom isn’t browning too rapidly.
Cook until the underside is a deep golden brown and the potatoes on the top are starting to look translucent, 15 min
If you feel adventurous, flip the Rosti and continue cooking. Otherwise, remove rosti onto a plate and flip back into the pan. Cook 5-7 minutes more
Top with cured salmon, crème fraiche and herbs.