In a medium saucepan, bring the 1/2 cup dry white wine, 2 tablespoons lemon juice and 1 medium shallot to a low simmer.
Whisk in the 1/4 teaspoon fine sea salt, 1/4 teaspoon ground white pepper and 1/3 cup heavy cream.
Reduce the heat to low, when it stops bubbling, slowly whisk in a few cubes of the 2 cups unsalted butter at a time until all are added and fully melted. The sauce will thicken. If you don't keep the temperature low and whisk continuously, the sauce will separate.
Pour the sauce through a fine mesh sieve to remove large pieces of seasoning or shallot. Serve immediately.
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Notes
This sauce is an emulsification, it can potentially separate. Whisk well or shake to recombine. Storage: Make it up to a day ahead of time, but add butter and gently reheat on the stovetop over low heat. Freezing: Freeze in an airtight container for up to 6 months. I also like freezing it in an ice cube tray and then popping them out into plastic bag so easy thawing.