Remove the tomatillo husks and rinse off the sticky coating. Quarter the tomatillos, stem the serrano, and peel the garlic.

Put the quartered tomatillos, stemmed serrano and peeled garlic in the saucepan with 1 cup (240 ml) water. Bring to a simmer, cover, and cook gently for 8–10 minutes, until the tomatillos are softened and olive green. Remove from the heat and leave uncovered to cool while preparing the remaining ingredients.

Roughly chop three-quarters of the onion (150 g); finely dice the remaining quarter (50 g) for serving. Chop the cilantro and divide it into two equal portions. Drain and rinse the beans and cut the lime into six wedges. On a separate board, trim visible fat from the beef, slice across the grain about ¼ inch (6 mm) thick, then cut into roughly ½-inch (1.3 cm) bite-size pieces. Wash hands, knife and any surfaces that touched raw meat.

Put the cut bacon in the unheated soup pot. Cook over medium heat, stirring regularly, for 8–12 minutes until browned and crisp. Lift onto the paper-towel-lined plate with the slotted spoon. Carefully pour off all but 1 tablespoon (15 ml) of bacon fat from the pot; let the excess fat cool before discarding.

Add 1 cup (240 ml) of the cold beef broth to the cooled tomatillo mixture. Once it is no longer hot, transfer the mixture and all its liquid to the blender with the roughly chopped onion and half the cilantro (about 10 g). Blend until smooth, following the blender manufacturer’s warm-liquid capacity and venting instructions. Never seal hot liquid in a blender; cool fully first if the blender is not rated for warm liquids.

Return the pot with the reserved bacon fat to medium heat. Add the beef, ¼ teaspoon of the salt and all the pepper. Cook, stirring, for 5–7 minutes, allowing the beef to release its juices; keep those juices in the pot. Pour in the blended tomatillo mixture and the remaining 3 cups (710 ml) beef broth, scraping any browned bits from the bottom. Bring just to a boil, reduce to a gentle simmer, partially cover, and cook for 10–15 minutes, until the small beef pieces are tender. Check the thickest pieces with a thermometer: beef must reach at least 145°F (63°C), followed by at least 3 minutes before serving; continuing the simmer covers that interval. Stir in the drained beans and simmer for 5 more minutes until thoroughly hot. Add up to 1 cup (240 ml) water if the broth needs loosening. Taste, then add only as much of the remaining ¼ teaspoon salt as needed.

Stir and divide the beef, beans and broth among six bowls. Top evenly with the reserved crisp bacon, finely diced onion and remaining cilantro. Serve one lime wedge with each bowl.