Set up a double boiler with simmering water in the bottom pot and a glass bowl on top.
2
Add egg yolk and heavy cream to the bowl. Whisk for 1-2 minutes until the cream begins to emulsify and thicken slightly.
3
Gradually add cold butter cubes while whisking continuously. Keep the heat gentle and patient, allowing the butter to incorporate slowly. The entire process takes about 4-4.5 minutes.
4
Once the sauce reaches a semi-thick consistency (not too heavy), continue whisking over low heat until the butter is fully incorporated. Continue whisking gently as the sauce cools slightly off the heat.
5
Season with white pepper, salt, and cayenne. Finish with lemon juice and mix gently. If the sauce becomes too thick before serving, warm it briefly over the double boiler to achieve the right pouring consistency.