8 tablespoonsunsalted butter (1 stick), cut into 8 pieces, at room temperature
1 to 2 teaspoons finely chopped fresh chervil (optional)
Freshly ground black pepper
Though prone to breaking (when the egg and butter separate), this sauce will hold together if you pay attention to the temperature and add the butter at a slow but steady pace. Once the eggs hit the heat, watch them closely so they don’t scramble. Serve Béarnaise sauce over Pepper-Crusted Filet Mignon.
1Fill a medium saucepan with 1 inch of water and bring it to a bare simmer over low heat.
2Meanwhile, combine the vinegar, wine, shallots, tarragon stems, and crushed peppercorns in a medium frying pan. Bring to a simmer over medium heat and cook until reduced to just over 2 tablespoons, about 10 minutes. Strain the vinegar mixture, pressing on the solids, through a fine-mesh strainer and into a medium heatproof bowl large enough to sit suspended over (but not touching) the water in the saucepan; discard the solids.
3Add the egg yolks to the vinegar mixture and whisk to combine. Set the vinegar-yolk mixture over the simmering water and cook, whisking constantly, until the yolks thicken and the mixture forms ribbons when the whisk is lifted from the bowl, about 3 to 4 minutes. (Check to make sure the water does not boil by periodically removing the bowl from the saucepan using a pot holder or dry towel. If the water boils, reduce the heat so the eggs do not curdle.)
4Whisk in the butter pieces one at a time, making sure each piece is incorporated before adding the next, until all of the butter has been added, about 2 minutes total. Remove the sauce from heat. (If the sauce is too thick, you can thin it with a few drops of water.) Whisk in the chopped tarragon leaves and chervil (if using) and season with salt and pepper. Serve warm.