2teaspoontarragon vinegar or just use white wine vinegar
1teaspooncold water
130grams (1stick + 1 tbsp)unsalted butter must be softened
3tablespoonfresh tarragon finely chopped
Instructions
Tarragon vinegar
Place the vinegar, diced shallot, and two stems of tarragon (or just the leaves) into a saucepan.
Boil the vinegar until it reduces in volume to 2 teaspoons, then strain and allow to cool completely (put it in the freezer for 5 minutes).
Béarnaise Sauce
Place the room-temperature egg yolks into a small heavy-based saucepan with the vinegar and a teaspoon of cold water. Whisk them together until fully incorporated.
Turn the heat to low. Gently warm the egg yolk mixture and whisk continuously. When it feels warm, but not hot, to the touch, add one cube of butter and whisk until it melts into the egg yolks.
Slowly keep adding butter, whisking in one small cube at a time. Monitor the heat and lift it off the stove if it ever seems to be on the verge of catching. If the surface ever starts violently steaming, it is too hot and will need a brief time out.
Once all the butter has been incorporated, remove it from the heat, and whisk in the chopped tarragon, and season with salt and black pepper.
Warm the serving jug in the microwave or pour the sauce into a thermos to keep it warm whilst serving.
Notes
Expert tips
This is a high-risk method if you do not have decent cookware. The saucepan needs to have good heat distribution and a heavy base. If it's one of those thin saucepans that heats up very fast and often burns things, it is not the right one for this recipe.
The butter needs to be at room temperature before you begin. I find this takes around an hour out of the fridge. It is at the right temperature when you press a finger to the surface and it leaves an indent.
TroubleshootingIf the sauce starts to really steam at any point, lift it off the stove and continue whisking until it cools slightly. Otherwise, the eggs can start to scramble. I sometimes have the sink filled with an inch of cold water just in case I need to quickly cool the saucepan down before resuming.