Combine the wine, vinegar, shallot and 1 tablespoon of the tarragon in a small saucepan over medium-high heat. Simmer until the mixture is reduced by half, about 2 minutes. Remove from the heat and let cool completely.
Place the egg yolks in a blender and add the cooled wine mixture. Purée for 30 seconds.
Melt the butter in a small saucepan over medium-high heat until very hot. With the blender running, pour the melted butter through the blender top, blending until the sauce is smooth and thickened. Remove from the blender and stir in the remaining tablespoon tarragon and season with salt and pepper. Set aside. (The sauce will continue to thicken as it stands.) |