Foolproof Béarnaise Sauce

Ingredients

• 1/4 cup white wine vinegar
• 1/2 cup dry white wine
• 3 sprigs tarragon, leaves finely minced, stems reserved separately
• 3 sprigs chervil, leaves finely minced, stems reserved separately
• 1 small shallot, roughly chopped
• 1/2 teaspoon whole black peppercorns
• 2 egg yolks
• Kosher salt
• 1 1/2 sticks unsalted butter

Directions

1. Add the vinegar, wine, herb stems, shallots, and black peppercorns to a small saucepan. Set it over medium-high heat and bring the mixture to a simmer, then adjust the heat so it stays gentle. Cook until the liquid has cooked down to about 1 1/2 tablespoons, about 15 minutes. Pour it through a fine mesh strainer into a small bowl, using the back of a spoon to press the solids so you get as much liquid as you can.
2. Pour the vinegar reduction into the bottom of a cup that just fits the head of your immersion blender, then add the egg yolk and a pinch of salt. Melt the butter in a small saucepan over high heat, swirling the pan the whole time, until the foam settles down. Pour the butter into a 1-cup liquid measuring cup.
3. Set the immersion blender head at the very bottom of the cup and switch it on. While the blender runs the whole time, drizzle in the hot butter slowly. The butter should blend into the egg yolk and vinegar reduction into a smooth emulsion. Keep pouring until every bit of butter has been added. The sauce should be thick and creamy. If it looks thin or runny, move it to a large bowl set over a pot of barely simmering water. Whisk hard and continuously until it thickens. Add salt to taste, then whisk in the chopped tarragon and chervil. Serve right away, or spoon it into a small covered pot and hold it somewhere warm for up to 1 hour before serving. Béarnaise cannot be cooled and reheated.