Prepare the dried chillies: Place the deseeded guajillo and ancho chillies in a heatproof bowl. Pour over boiling water until they are fully submerged, then set a small plate on top to keep them under the water. Leave for 15–20 minutes until the chillies are soft and pliable — they should feel like softened leather when you press them.

Toast the beef: While the chillies soak, pat the beef chunks dry with kitchen paper. Season generously with salt and pepper. Heat the olive oil in a large, heavy-based frying pan over a high heat until it shimmers and a wisp of smoke rises. Sear the beef in a single layer — work in two batches if needed — for 2–3 minutes per side until each piece is deep mahogany brown with a crisp crust. You should hear a satisfying sizzle; if the pan goes quiet, it's too crowded. Transfer the seared beef to your slow cooker insert.

Blitz the sauce: Drain the softened chillies (reserving a little soaking liquid) and tip them into a food processor or blender. Add the chopped garlic, onion, cumin, oregano, smoked paprika, ground cloves, apple cider vinegar, and 125 ml of the beef stock. Blitz until you have a smooth, deep red purée — it should look like a thick tomato paste with a rich, smoky aroma. If it's too stiff to blend, add a splash of the reserved chilli soaking water.

Combine in the slow cooker: Pour the chilli purée over the beef in the slow cooker. Add the remaining 125 ml of beef stock, the bay leaves, and an extra pinch of salt. Stir gently to coat every piece of meat in that gorgeous red sauce. The sauce should come about halfway up the beef — if it looks dry, add a splash more stock.

Cook low and slow: Cover the slow cooker and cook on low for 6–8 hours, or on high for 4–5 hours. After about 4 hours on low, your kitchen will fill with a deep, earthy, slightly sweet aroma. The beef is ready when it yields easily to a fork and shreds with almost no resistance — it should feel like pulling apart warm butter.

Shred and finish: Using two forks, shred the beef directly in the slow cooker. Stir the shreds through the cooking liquid so every strand is coated. Taste and adjust the seasoning — you might want another pinch of salt or a splash more vinegar for brightness. If the sauce seems too thin, leave the lid off for 10–15 minutes on the high setting to let it reduce slightly; you'll see it thicken and become glossier.

Rest before serving: Let the shredded barbacoa sit in the warm slow cooker with the lid on for 10 minutes. This resting time allows the fibres to relax and the sauce to cling beautifully to the meat rather than pooling at the bottom of the bowl.