1. Using a mandolin, slice the potatoes 1mm thick. Put the potato slices into stacks, and then slice as thin as possible.
2. Place into a large bowl filled with ice-cold water for 5 minutes. This will remove all the excess starch from the potatoes and help to make them crispy.
3. Remove and drain the potatoes, then pat dry with kitchen paper.
4. Place the dried potatoes in a medium sized bowl, and then add the melted butter and season with salt and pepper.
5. Preheat the oven to 180C.
6. Heat a medium sized non-stick frying pan, add the potatoes evenly to the pan, and gently fry for 5 minutes, pressing down the potatoes while you fry.
7. Place the rosti into the oven in the frying pan and cook for 10 to 15 minutes or until slightly golden. Remove from the oven and flip the rosti. Place back in the oven for a further 10 to 15 minutes or until golden and crispy.
8. Remove from the oven and allow to cool slightly.
9. Cut the rosti into 4.
10. Divide between 4 plates and serve with the crème fraiche, chives and sturgeon.