- 1/4 cup white wine vinegar
- 1/2 cup dry white wine
- 4 sprigs tarragon, leaves minced, stems reserved
- 1 small shallot, roughly chopped
- 1/2 tsp whole black peppercorns
- 2 egg yolks
- Kosher salt
- 12 Tbsp (1 1/2 sticks) unsalted butter
In a small saucepan over medium-high heat, combine vinegar, wine, herb stems, shallots, and black peppercorns. Bring to a simmer and lower heat to maintain a gentle simmer. Cook until reduced to about 1 1/2 tablespoon of liquid, about 15 minutes. Carefully strain liquid through a fine mesh strainer into a small bowl, pressing on solids with back of a spoon to extract as much liquid as possible.
Combine vinegar reduction, egg yolk, and a pinch of salt in bottom of a cup that barely fits head of an immersion blender. In a small saucepan over high heat, melt butter, swirling constantly, until foaming subsides. Transfer butter to a 1-cup liquid measuring cup.
Place head of immersion blender into bottom of cup and turn it on. With blender constantly running, slowly pour hot butter into cup. It should emulsify with egg yolk and vinegar reduction. Continue pouring until all butter is added. Sauce should be thick and creamy. If it is thin and runny, transfer to a large bowl set over a pot of barely simmering water. Whisk constantly and vigorously until sauce is thickened. Season to taste with salt.
Whisk in chopped tarragon. Serve immediately, or transfer to a small lidded pot and keep in a warm place for up to 1 hour before serving. Béarnaise cannot be cooled and reheated.