Step 1

Add chopped onions to 1/4 of the butter in a pan. Over low heat, let the butter melt with the onions. Careful to not toast the onions - onions will turn translucent but there shouldn't be browning at all. The butter should also come to a gentle sizzle.

Step 2

Once onions turn translucent, or you start smelling it, add in the rest of the butter. Still keeping a low heat, allow butter to melt slowly. When all of the butter has almost melted, turn off the heat.

Step 3

Add tarragon, parsley, sage (and basil if using), anchovies, ground nutmeg, walnuts, capers, ground pepper. Blend this up, so you get a butter cream. Optional: pour this mixture in a pouring or measuring cup for the next step, so it's a less messier process.

Step 4

In a separate bowl, add egg yolk, mustard, maggi seasoning sauce (or worcestershire sauce), and the vinegar. Use a whisk or hand mixer to beat this mixture. Gradually pour in the butter cream from earlier. Eventually this will become a thick creamy consistency, much like mayonnaise.

Step 5

Pour 2/3rds of the mixture into a saucepan. Meanwhile, prepare a bowl filled with cold water. Your pan should be able to sit in the bowl easily.

Step 6

Heat the saucepan over low to medium heat, and continuously stir. Do not let this come to a boil. Stir until it breaks and turns into a crumbly liquid. It should look "ruined".

Step 7

Once it turns crumbly, immediately take the saucepan off the heat and place it in the bowl of cold water. Continue to stir to stop the cooking process. After about 30 seconds, add this mixture back into to the leftover mayonnaise that we did not heat up.

Step 8

Give that a whisk to combine the two sauces together. Sauce is done!