The meat is cooked in an adobo, a sauce made with chillies, spices and vinegar. The birria can be eaten in a bowl like a soup, or in tacos or quesadillas (see Tip). You can make the adobo a day ahead.
Put the beef, onion and pepper in a wide-based saucepan ... Use as above. For extra special tacos, add guacamole, salsa, grated cheddar and some fresh coriander. Any leftover soured cream can ...