Melt the butter in a microwave-safe bowl.
Place the egg yolk, vinegar, salt and water into a metal bowl and whisk for a couple of minutes until it turns frothy.
Place a small saucepan of water over a medium-low heat until simmering. Place the bowl with the whisked egg yolk over the saucepan and whisk constantly for around 5 minutes until pale and thick.
Remove the bowl from the saucepan. Gently and slowly pour the melted butter into the bowl, whisking all the time, until the mixture resembles a thick sauce. If the mixture separates, add in 1 tablespoon of cold water and continue whisking thoroughly until it comes back together.
Add the lemon juice and cayenne pepper to the hollandaise sauce. Taste and add more if needed.
Keep the sauce warm by turning the heat off the stove and placing the bowl over the saucepan of warm (but no longer simmering) water.
Use a fork to break each of the English muffins in half and toast them in the toaster or in a dry frying pan.
Bring a large saucepan of water to a boil over a medium-high heat and drop each of the eggs in. Leave the eggs in the simmering/boiling water for 2-3 minutes until poached to your liking.
Spread 1 tablespoon of cream cheese on top of each toasted muffin half and top with a slice of smoked salmon.
Place 1 poached egg on top of each slice of salmon and spoon over some hollandaise sauce.
Sprinkle on top some fresh chives and serve immediately whilst hot.