
Melt ½ cup unsalted butter in the microwave in a microwave-safe bowl. You can also do it in a small saucepan if you prefer.
Separate 3 large egg yolks and add them to a container like a Mason jar. You want the head of the immersion blender to fit in the container.
Add 1 teaspoon lemon juice, ¼ teaspoon salt, and a pinch cayenne pepper. Position the immersion blender in the container.
Slowly stream in the melted butter while constantly blending. Make sure to gently move the blender around to ensure even blending. This should take around 30 seconds to 1 minute.
Give it a quick taste and adjust the flavors if needed. Serve the sauce warm.