Preheat the oven to approx. 175 ° (convection 150 °).
Mix the flour, eggs and milk until smooth, season with salt and pepper and leave to soak for about 10 minutes.
Line the oven`s drip pan with parchment paper and heat it in the oven for about 5 minutes. Stir mineral water into the batter. Spread a thin layer of oil on the baking paper. Pour the batter evenly on top. Bake in the oven on the lower rack for about 12-15 minutes until golden brown.
Cut the chives into rolls. Let the pancakes cool a little and brush with horseradish and crème legère. Sprinkle with chives, spread the salmon on top and roll up the pancake tightly from the long side.