poach the egg
Pour about 7-10 cm water into a saucepan. Set the saucepan over medium heat and bring to a light simmer (the water temperature should be around 80 - 90 °C / 175 - 195 °F). Crack one of your eggs into a coffee cup. Stir the water with a spoon to create a whirlpool. Tip the egg into the center of the swirling water. Cook for about 3 - 4 minutes just below the simmering point. Remove the eggs with a skimmer. To check if the eggs are done, remove one from the water with a spoon and give it a gentle push with a finger. The egg white should be nice and firm and the yolk still soft.
Meanwhile prepare the hollandaise sauce. Whisk the egg yolk and white balsamic vinegar (or lemon juice) in a small glass bowl until the mixture is thickened. Place the glass bowl over a saucepan with simmering water (make sure the water doesn't touch the bottom of the bowl). Whisk the egg yolks rapidly and be careful not to get the eggs too hot. Remove from the heat and slowly drizzle in the melted butter. Whisk until the sauce is thickened. Season to taste with salt, pepper and a pinch of cayenne pepper. It the sauce gets too thick, add a few drops of cold water before serving. Leave the hollandaise sauce in a bowl over the saucepan until serving.
To serve slice each bagel and toast it. Spread the cream cheese over the toasted bagel. Add a slice of smoked salmon and thinly sliced gherkin. Place the poached egg over the gherkins and top with homemade hollandaise sauce. Complete sandwich with top of bagel. Enjoy.