Step 1

Place the butter in a small pan and melt it over a low heat. (Don't allow the butter to brown and turn off the heat as soon as the butter is just melted.) (see note 2)1 stick unsalted butter

Step 2

Whilst the butter is melting, put the egg yolks, lemon juice, salt (if using) and pepper into a measuring jug that the head of your immersion blender fits into. (see note 3)3 egg yolks4 tsp lemon juice¼ tsp saltpinch pepper

Step 3

Blend the egg yolk mixture for a minute, until it lightens in colour and is well combined.

Step 4

Keeping the blender in the jug, and with it running on the slowest setting, very slowly drizzle the hot melted butter over the egg mixture. (see note 4)

Step 5

As the sauce combines move the blender up through the sauce. (see note 5)

Step 6

Check the sauce, it should be slightly lemony and lightly seasoned.

Step 7

You can now add extra lemon, salt and pepper to taste. Add as required and give it a quick blend to combine.

Step 8

This is best served immediately but if that isn't possible place the jug in a bowl of body temperate water for up to an hour.