A proper hollandaise is creamy and smooth, with a well-balanced flavor of egg, butter, and lemon.

Melt 225 g of butter in a small saucepan, then pour it into a measuring cup, leaving the white liquid (milk protein) behind in the pan.
Combine 3 egg yolks, 1 tbsp of lemon juice, and 1 tbsp of warm water in an immersion blender container.
Place the immersion blender in the container and start blending - then slowly pour the butter into the container while continuing to blend. Once all the butter is mixed in and the sauce has thickened, pour it into a serving bowl or saucepan. Be careful when keeping it warm, as the sauce can separate.
Season to taste with salt and cayenne pepper, or a bit more lemon juice if desired.