Step 1

Cut 2 sticks unsalted butter into tablespoon-sized pieces. Place on a plate and freeze until ready to use.

Step 2

Prepare the following, adding them to a small saucepan as you complete them: Finely chop 1 small shallot until you have 2 tablespoons. Finely grate the zest of 1/2 medium lemon until you have 2 teaspoons zest. Juice the lemon until you have 2 teaspoons juice, then reserve the lemon. Coarsely crush 1 teaspoon whole black peppercorns.

Step 3

Add 1/4 cup dry white wine, 1/4 cup white wine vinegar, and 1 bay leaf. Bring to a simmer over medium-low heat. Continue to simmer until the liquid is reduced to about 2 tablespoons, about 5 minutes. Add 3 tablespoons heavy cream and simmer until the cream is slightly thickened, about 3 minutes more. Meanwhile, fit a fine-mesh strainer over a small heatproof bowl that fits onto the saucepan without touching the bottom.

Step 4

Pour the mixture through the strainer and press onto the solids to extract as much liquid as possible. Rinse the saucepan and add about 1 1/2 cups water. Bring to a boil over medium-high heat, then reduce the heat to maintain a simmer.

Step 5

Fit the bowl onto the saucepan, making sure the bottom isn’t touching the water. While whisking continuously, add the butter one piece at a time, making sure each piece is completely melted before adding the next, 10 to 12 minutes total. If you are unsure if your sauce is getting too hot, a good way to check is to stick your finger in the sauce. If the sauce is too hot to the touch, then remove it from the heat for a few seconds. When all the butter is added, the sauce should be thickened slightly, enough to coat the back of a spoon.

Step 6

Remove from the heat. Add 1/2 teaspoon kosher salt and a squeeze of lemon juice. Taste and season with more kosher salt or lemon juice as needed.

Step 7

To keep the sauce warm, keep the bowl on the saucepan but remove the saucepan from the heat. Whisk occasionally to keep the emulsification. If the sauce does separate, whisk in more heavy cream or water 1 tablespoon at a time until it comes together again. This can only be done once.