Bring a large pan of water to the boil, and add the vinegar, then lower the heat to a gentle simmer. Slowly stir the water and create a vortex. Crack an egg into a cup then drop the egg into the centre of the pan.
Poach for four minutes then remove using a slotted spoon, onto some kitchen paper. Repeat with the remaining eggs.
Toast the sourdough and top with a little spinach if you want to use it, then lay on the smoke salmon.
To serve, add the eggs and cover with Hollandaise sauce and season.