Who doesn't love sauces made from avocado? I do, in all their forms, even if it's a guacamole with underripe styrofoam tomatoes and pungent lemons. Or a tomatillo salsa mixed with avocado. Or simply a thin avocado and lime puree. But my favorite version hits all the notes I'm looking for. —prettyPeas
chopped cilantro, some stems included
Roast the serrano pepper over a gas burner (or grill, or broil) until the outside begins to turn black and blister. When cool remove blistered skin. I usually put it in a covered jar while cooling so the steam helps loosen the skin. Chop finely, removing veins and seeds if you don't like heat. I usually remove seeds for texture reasons, but leave the veins because I like the spiciness.
Press or chop garlic. Add garlic, salt, ~1/4 serrano pepper, and ~2 T chopped cilantro to a mortar and pestle and pound to a paste.
Scoop avocado into serving bowl and squeeze 1/2 a lime over the top. Pour the paste on top and mash the mixture until evenly combined.
Add remaining cilantro, stir, and taste. Add more lime, salt or serrano if desired. I usually add more of each, and if I'm not serving right away I add the extra lime juice to the top without stirring afterwards to leave a layer of protection between the avocado and all that browning oxygen in the air.