Preheat the oven to 180c.
Grate the potatoes (skin and all) then place in a large sieve set over a bowl. Add ½ tsp of salt and leave for 10 minutes and leave for 10 minutes, then transfer to a clean tea towel and squeeze out as much liquid as possible.
Place the potato in a clean bowl and add the seasoning, baking powder, plain flour and egg. Stir together.
Heat the oil in a 9inch non-stick frying pan and add the grated potato mixture, packing it down as much as possible in one even layer. Cook over a medium heat for around 5 minutes or until crisp and golden then turn and cook for a further 5 minutes on the other side (use a plate to turn out then return to the pan if easier).
Remove the woody ends from the asparagus and toss in a little oil, then season.
Transfer the rosti to a baking tray along with the asparagus and cook in the oven for around 10 minutes, until the rosti is thoroughly cooked through and the asparagus tender (alternatively you could boil or steam the asparagus).
Meanwhile, bring a saucepan of water to the boil and add the 6 eggs. Cook for 6 minutes then remove and plunge into cold water. Peel off the shells then slice each one in half.
Combine the crème fraiche, lemon juice and zest and a little black pepper.
To assemble place the rosti on a serving platter and dollop the crème fraiche over the top. Add waves of smoked salmon, followed by asparagus tips then the jammy eggs. Finish with dill sprigs or chives, as well as some extra cracked black pepper and lemon juice, if you like.