Birria Tacos

Cut the beef into 5 cm chunks and season with 1 tsp of the salt. Heat a dry frying pan over a medium heat and toast the guajillo, ancho and árbol chillies for 20 to 30 seconds per side, pressing them down, until fragrant and slightly puffed. Do not let them scorch, or the broth will turn bitter.

Snip the stems off the chillies, shake out the seeds and put them in a bowl. Cover with 500 ml of boiling water and soak for 20 minutes, until soft. Heat the oven to 160°C (140°C fan)/gas 3.

Heat the oil in a large flameproof casserole over a medium-high heat and brown the beef in batches, 3 to 4 minutes per batch, until deeply browned. Lift out and set aside.

Quarter one of the onions and put it in a blender with the softened chillies, 250 ml of their soaking water, garlic, tomatoes, ginger, vinegar, cumin, oregano, cloves, peppercorns and the remaining 1 tsp salt. Blend for 2 minutes until completely smooth, then press through a sieve into the casserole.

Return the beef to the pot with the stock, cinnamon stick and bay leaves. The liquid should come almost to the top of the meat. Bring to a simmer, cover tightly and cook in the oven for 3 to 3 1/2 hours, stirring once halfway, until the beef collapses when pressed with a fork.

Lift the beef onto a board and shred it with two forks, discarding any fat and gristle. Strain the cooking liquid through a sieve into a pan, discarding the bay, cinnamon and solids. Skim the red fat from the surface into a bowl and keep it for frying the tortillas. Squeeze the juice of one lime into the broth, season to taste and keep hot.

Heat a large frying pan or griddle over a medium-high heat. Dip a tortilla in the reserved fat on both sides and lay it in the pan. Scatter about 20 g of mozzarella over one half, top with 3 tbsp of shredded beef and fold over. Fry for 1 1/2 to 2 minutes per side, until crisp and the cheese has melted. Repeat with the rest, keeping finished tacos warm in a low oven.

Finely chop the remaining onion and the coriander. Serve the tacos with the onion, coriander, remaining limes cut into wedges and mugs of the hot broth for dipping.