Place the Roma tomatoes, onion wedges, and garlic on a tray. Drizzle with neutral oil and roast under a hot broiler for 8–12 minutes, turning once, until the tomatoes soften, collapse slightly, and develop charred spots. The tomatoes should look roasted and juicy, not dry. Do not burn the garlic; bitter garlic will flatten the broth. Broiling rather than simmering the tomatoes and aromatics concentrates their sugars and adds a light char that a purely blended-and-simmered base wouldn't have — this early step is quick but sets the tone for the broth's overall depth.

Toast the guajillo and pasilla or ancho chile in a dry skillet over medium heat for 10–15 seconds per side, just until fragrant and flexible. Do not let them blacken or smoke. Cover the toasted chiles with hot water and soak for 10–15 minutes until softened. Drain before blending. The brief dry toast blooms each chile's specific aromatic character before rehydration — guajillo's fruity tang and pasilla or ancho's darker, raisin-like sweetness both come through more clearly toasted than simply soaked from raw.

Blend the roasted tomatoes, onion, garlic, softened chiles, chipotle peppers, adobo sauce, tomato paste, cumin, Mexican oregano, smoked paprika, salt, black pepper, and 300ml chicken stock until completely smooth. Strain through a fine sieve if the mixture has visible chile skin or tomato skin. The base should be vivid red-orange, smooth, and thick. A high-powered blend here matters for the finished soup's texture — any unblended skin fragments left in will remain as a slightly gritty presence in an otherwise smooth, glossy broth.

Heat a large pot over medium heat. Add a thin film of neutral oil if the pot is dry. Pour in the blended tomato-chipotle base and cook for 5–7 minutes, stirring often, until it darkens slightly, thickens, and smells roasted instead of raw. This step matters. If you skip it, the soup tastes like blended salsa dumped into stock. Frying the paste briefly before any stock is added lets its flavour compounds bloom directly in fat rather than diluting immediately into liquid — this is the exact same principle that separates a rounded, roasted-tasting sauce from a flat, dusty one.

Add the remaining chicken stock and bring to a simmer. Add the chicken and bay leaf. Reduce the heat to medium-low and simmer gently for 18–22 minutes, until the chicken reaches 74°C internally and shreds easily. Remove the chicken and rest for 5 minutes. Discard the bay leaf. Shred the chicken into medium strands. Return the shredded chicken to the soup and simmer for another 5 minutes. Finish with lime juice and adjust salt. The broth should be deep brick-red, glossy, and spoonable — not thick like enchilada sauce and not watery. A gentle simmer rather than a hard boil keeps the chicken tender and the broth clear rather than clouded, and the 5-minute rest before shredding firms the meat's fibres just enough to pull into clean strands.

Stack the corn tortillas and cut them into thin strips, about 1cm wide. Heat neutral oil in a saucepan to 175–180°C. Fry the tortilla strips in batches for 60–90 seconds, stirring gently, until golden, crisp, and bubbling slows. Transfer to a rack or paper towel-lined tray and season immediately with salt. Do not crowd the oil. Pale soft strips are useless here. They need to be crisp enough to stand upright above the broth. Salting immediately while the strips are still hot and glistening with oil is what allows the seasoning to actually adhere — strips left to cool first won't hold salt nearly as well.

Cut the dried guajillo or pasilla chiles into thin strips. Briefly fry them in 15ml hot tortilla-frying oil for 5–10 seconds, just until glossy and slightly darker. Remove immediately and season with a pinch of salt. They burn fast. If they turn almost black, throw them out and start again. Using the same oil already hot from frying the tortilla strips saves a step and means the chile strips fry in oil that's already carrying a light corn flavour, but the window here is genuinely narrow — these thin dried chiles go from glossy to scorched in a matter of seconds.

Dice the avocado shortly before serving so it stays bright green. Loosen the sour cream with a few drops of water or lime juice if needed so it can swirl into the soup. Crumble the cotija and pick the cilantro leaves. Timing the avocado dicing to as close to serving as possible limits its exposure to air and the oxidation that dulls its colour, keeping the diced cubes visually vivid against the red broth.

Ladle the hot tomato-chipotle broth and shredded chicken into four bowls. Add diced avocado across the surface. Swirl sour cream through the broth in thick white streaks. Scatter cotija and dried chile strips. Pile crispy tortilla strips generously in the centre of each bowl, leaving some standing upright above the broth. Finish with cilantro leaves and lime wedges on the side. Serve immediately before the tortilla strips soften. Leaving some strips standing genuinely upright, rather than fully submerging all of them, is the plating detail that preserves the soup's defining visual signature — strips buried completely in hot broth begin softening within minutes.