Gather all ingredients before starting the recipe.
Combine 2 whole egg yolks, the juice of 1/2 medium lemon, 1 large pinch kosher salt 1/2 tsp Asian chili sauce (hot) a in a cup that barely fits the head of an immersion blender.
Cut 1/4 lb unsalted butter into 3 pieces and transfer to a one cup microwave safe glass measuring cup. Heat on high for one minute, or until the butter starts to foam.
Place head of immersion blender into the bottom of the cup and turn it on.
With the blender constantly running, slowly pour the hot butter into the cup. Continue pouring until all the butter has been added. The sauce should be thick and creamy, able to coat the back of a spoon.
If it's too thick whisk in a small amount of warm water 1 tablespoon at a time, until you have reached the desired consistency.
Serve immediately, or pour into a small lidded pot and keep in a warm place for up to an hour.