2.

Place head of immersion blender into the bottom of the cup and turn it on. With the blender constantly running, slowly pour hot butter into cup. It should emulsify with the egg yolk and lemon juice. Continue pouring until all butter is added. Sauce should be thick and creamy. Season to taste with salt and a pinch of cayenne pepper or hot sauce (if desired). Serve immediately, or transfer to a small lidded pot and keep in a warm place for up to 1 hour before serving. Hollandaise cannot be cooled and reheated. Check here for a full video walkthrough of the process.