Chorizo and Potato Tacos (Tacos de Chorizo y Papa)

Combine half of the onion and half of the cilantro on a cutting board (or in a molcajete, or mortar, if you have one) along with the chile and salt. Mince together with a large knife and mash with the side of the knife to create a paste (or mash with the pestle). Transfer to a bowl. Score the avocado, twist the halves apart, and scrape the flesh out of its skin with a large spoon into the bowl. Add the remaining onion and cilantro and stir together with a fork.

Peel the potatoes and cut them into 1⁄2-inch dice. Cook in a saucepan of boiling salted water until they are just cooked through and still hold their shape, about 5 minutes. Drain.

Remove the casings from the chorizo and crumble (Mexican) or finely chop (Spanish) the meat. Cook the chorizo in a large skillet (add a tsp. of oil if using Spanish chorizo) over medium heat, stirring, for 5 minutes. Add the potato and oregano and cook, stirring, for 5 minutes. Season with salt to taste.

Make tacos with the tortillas, guacamole, and queso fresco, if using.