Combine the ingredients

• Place the egg yolks, lemon juice, shallot vinegar, water and salt in a tall container or bowl.
• Add the melted butter.

Heat to 70 °C

• Set the container over a saucepan of gently simmering water, or heat gently while monitoring with a thermometer.
• Bring the mixture to 70 °C.

Blend and hold

• Blend with an immersion blender until thick and emulsified.
• Keep at 70 °C for 30 minutes, shaking the container occasionally.