Preheat the oven to 200°C.
Peel the cucumber, remove the seeds in the centre and cut into small dice. Sprinkle with salt and to draw out the water and set aside.
Place the egg yolks, mustard, salt and piment d'Espelette in a bowl and combine. Whisk in the oil a little at a time until you have a smooth and shiny mayonnaise. Add the vinegar and the horseradish and then check the seasoning. Spread the mayonnaise between two bowls. Add a little water to one bowl to loosen the mayonnaise and create a sauce. Set aside.
Use a stainless steel serving ring to create circles of grated parmesan on a baking sheet. Transfer to the oven and cook for 4 to 5 minutes.
Drain the diced cucumber and then mix it with the thick mayonnaise.
Serve the salmon on a bed of diced cucumber and then place a parmesan tuile on top. Finish with a drizzle of the sauce, a little fresh dill and a pinch of piment d'Espelette.
«Vary the flavour of your mayonnaise by using different types of mustard.»