In a small stainless steel sauce pot add shallots and vinegar and bring to a simmer. Continue to reduce liquid until less then a 1/4 teaspoon of liquid remains. * If using lemon juice, be careful not to cook on too high a heat as it can burn and taste bitter.
Once liquid is reduced, remove from heat and allow to sit while prepping the other ingredients.
In a blender add egg yolks and cracked pepper. Add cooked shallot mixture and blend together on medium speed. Slowly add melted butter in a thin continuous stream.
Turn blender up to highest speed and add in tarragon. Stop blending once sauce has thickened. Season to taste with salt and more cracked pepper as needed.