Combine the sliced red onion, 120g hot water, 60g vinegar, 1 tsp sugar, and 1 tsp kosher salt in a bowl or jar, then toss well and press the onion down so it sits fully submerged. Leave it to stand for at least 30 minutes while the rest of the tacos come together, until the slices have softened, turned bright pink, and lost their harsh raw bite. Drain just before serving. That short hot pickle is what gives the tacos a sharp, tangy counterpoint without any raw-onion sting.

Place the 500g tomatillos, 1–2 serrano chiles, ¼ white onion, and 1 garlic clove in a saucepan, cover with water, and bring to a simmer. Cook for 8–10 minutes, until the tomatillos turn from bright green to olive green and are fully tender but not disintegrating. Drain well, then blend with the 10g cilantro and ½ tsp salt until smooth or lightly textured, adding 1–2 tbsp water only if the blender stalls. Taste and adjust the salt; the salsa should be spoonable, not watery. That thick, concentrated texture is what lets a small spoonful flavour a taco without wetting the tortilla.

Cover the 500g potatoes with cold salted water, bring to a boil, then simmer for 12–15 minutes until fully tender. Drain very well and let them steam dry in the colander for 1–2 minutes. Heat 1 tbsp lard or oil in a skillet over medium heat, add the 40g chopped onion, and cook for 3–4 minutes until soft and translucent. Add the potatoes and mash directly in the pan until mostly smooth with a little texture, season with ¾ tsp salt, and stir for 1–2 minutes until the mixture holds its shape on a spoon. Cool slightly. That steam-dried, pan-thickened mash is what keeps the filling from weeping into the tortilla.

Heat 1 tbsp lard or oil in a small skillet over medium heat, add the 30g chopped onion, and cook for about 3 minutes until soft. Add the 350g refried beans and stir constantly until hot and thick. If they are too stiff to stir, loosen with 2–4 tbsp water or bean cooking liquid, a spoonful at a time, keeping them thick and spreadable rather than runny. Taste for salt, adding only if needed, then cool slightly. That thick, spreadable consistency is what stops the beans from seeping through the folded tortilla as the tacos rest.

Toast the 2 stemmed, seeded guajillo chiles in a dry skillet for 5–10 seconds per side, just until fragrant, since scorched chiles turn bitter. Cover them with hot water, soak for 10 minutes until softened, then blend with the 2 Roma tomatoes, 1 garlic clove, 30g onion, ½ tsp salt, and 60–120g water until smooth. Heat 1 tbsp lard or oil in a skillet over medium heat, add the sauce, and cook for 5–7 minutes, stirring often, until it darkens slightly, loses its raw smell, and thickens. Stir in the 250g chicharrón prensado and cook 3–5 minutes more until the pork softens and the mixture is moist but not loose, with no sauce pooling in the pan. That reduction is what leaves a rich, cohesive filling that stays inside the fold.

Combine the 180g neutral oil (or 90g neutral oil and 90g melted lard), 3 stemmed, seeded guajillo chiles, ½ sliced white onion, 2 lightly crushed garlic cloves, and ½ tsp salt in a saucepan. Heat over low to medium-low heat for 8–10 minutes, until the mixture sizzles gently and the oil turns orange-red, with the onion softened and nothing browned deeply or burnt. Remove from the heat, then strain for a cleaner oil or leave the softened onion in to layer into the basket; either way keep the oil warm, not smoking hot. That gentle infusion is what stains the tortillas without frying them.

Warm and Fill the Tortillas

Warm the 16 small corn tortillas on a comal or skillet just until soft and pliable, or wrap and steam or microwave them briefly, until they fold without cracking. Keep them covered in a towel while you work. Fill 6 tortillas with mashed potato, 5 with refried beans, and 5 with chicharrón, using about 2 heaped tablespoons per taco spread across the centre, then fold each into a half-moon. Do not overfill. That restraint is what stops the tacos from bursting when they are stacked and steamed.

Pack and Rest the Basket

Line a basket, deep bowl, Dutch oven, or small cooler with a large sheet of parchment or butcher paper, then a clean kitchen towel. Brush or lightly dip each taco in the warm chile oil until it takes on a light orange sheen without being drenched. Lay a few softened onion slices in the bottom, pack the tacos in snug layers with more onion and a little oil between them, top with the remaining onion and oil, then fold the paper and towel over to enclose and cover tightly. Rest for at least 30 minutes, ideally 45–60 minutes. That rest is what softens the tortillas, lets the oil penetrate, and builds the classic basket-taco texture.

Serve

Open the basket and lift the tacos out carefully; they should be soft, moist, and lightly oily, never crisp. Serve 4 tacos per person, topped modestly with a spoonful of salsa verde and a few slices of drained pickled red onion. Keep the garnishes restrained, since a heavy spoonful would drown the delicate corn and hide the fillings. That light hand is what keeps the steamed, chile-stained taco the focus of every bite.