Make potato rosti

Preheat oven to 100°C. Use the coarse side of a grater to grate the potatoes. Place in a colander and add the onion.

Use your hands to squeeze out as much excess liquid as possible. Transfer to a medium bowl. Add the melted butter and stir to combine. Season well with sea salt flakes and freshly ground black pepper.

Add enough oil to a large non-stick frying pan to reach a depth of 1cm and place over medium-high heat. Spoon two ½-cup portions of potato mixture into the pan. Use an egg lifter to flatten each portion to a 10cm disc. Cook for 3-4 minutes each side or until golden brown and cooked through. Use the egg lifter to transfer to a plate lined with paper towel. Place in warm oven. Continue in 3 more batches with remaining potato mixture, adding and reheating more oil if necessary.

Arrange two röstis on each serving dish. Top with avocado, smoked salmon, crème fraîche and red onion. Sprinkle with chives. Serve immediately with lemon wedges.