1. In a small saucepan combine shallots, vinegar, wine and tarragon stems. Bring to a boil. Reduce over medium heat for about 4-5 minutes or until almost all the liquid has evaporated and just a couple of tablespoons remain.
2. Remove from the heat and discard the tarragon stems. Cool slightly.
3. You can place the butter in a glass measuring cup/pitcher and melt it in the microwave in small intervals until hot and foamy or in a saucepan over low heat.
4. Continue using the traditional method or immerse blender or blender method.

Traditional Method:

1. Fill a small saucepan with about two inches of water. Bring to a boil over medium-high heat.
2. In a heat-resistant bowl, combine the cooled shallot mixture, water, egg yolks and salt.
3. Place the heat-resistant bowl over the saucepan of boiling water and turn the heat down to low. Make sure the bowl doesn’t touch the water.
4. Whisk the mixture until thick and creamy, about 5 minutes.
5. Gradually whisk in the melted butter, about a teaspoon at a time until the sauce begins to emulsify, then whisk in the remaining butter in a slow stream whisking until completely incorporated. Remove from the heat.
6. Stir in the tarragon and season to taste. Serve.
7. This sauce cannot be reheated, however it can be kept warm in a thermos or in a sous vide bath at 130ºF for about 3-4 hours.

Immersion Blender Method:

1. Place egg yolks, water, salt and cooled shallot mixture in a jar/container that will fit the immersion blender all the way to the bottom.
2. Place the head of the immersion blender at the bottom of the jar and turn it on for about 30-45 seconds to combine the mixture.
3. With the immersion blender running, slowly in a thin stream, pour in the melted butter. A thick sauce will form as the ingredients emulsify. If the mixture seems too thick, add a tablespoon of wine or water.
4. Stir in the finely minced tarragon and season with salt to taste. Serve.

Regular Blender Method

1. In the jar of a blender, place the cooled shallot mixture, water, egg yolks and salt. Blend for about 30-45 seconds.
2. With the blender running, slowly in a thin stream, pour in the melted butter through the opening in the lid. A thick sauce will form as the ingredients emulsify. If the mixture seems too thick, add a tablespoon of wine or water. Stir in the tarragon and season to taste and serve.