Adapted from
Leite’s Culinary and
The New Portuguese Table (Clarkson Potter) by David Leite
The original recipe says to use either a regular blender, or hand blender. Because milk is more liquid than egg yolks, expect a bit of splattering, which happened even when I used the relatively small pouring hole in my blender. If you have a small mesh strainer, you could put it over the hole to mitigate that. And wear an apron.
This would certainly work with any other fresh herb. And if you’re interested in the science of this emulsified sauce, and other variations, you can read more about them at the link above.