Rinse the asparagus, peel the lower third. Heat the butter in a pan, sauté the asparagus briefly, add a little salt and two tablespoons of water, with the lid closed, cook for two to three minutes, depending on the thickness of the sticks, drain and pat dry with kitchen paper.
At the same time, heat water with a dash of white wine vinegar in a saucepan. Beat the eggs one by one in a cup and carefully pour them into the hot water, pull the egg white around the yolk with a spoon. Poach for about three to four minutes, lift out of the water and let drain briefly.
Halve the roll, toast it and cover it with smoked salmon and asparagus when it has cooled down a little, place the poached egg on top and season with salt and pepper.