½ pound beef tenderloin, halved lengthwise into 2 long pieces
2 teaspoons kosher salt, divided
1 teaspoon freshly ground black pepper
2 small, ripe avocados--halved, pitted and roughly chopped
½ small white onion, roughly chopped
1 small poblano chile or ½ small green bell pepper, roughly chopped
½ cup fresh cilantro
1 small jalapeño, roughly chopped
1 garlic clove, roughly chopped
3 tablespoons distilled white vinegar
Juice of 1 lime
¼ cup canola or grapeseed oil, divided
Four 8-inch flour tortillas
2 cups shredded good-quality melting cheese, such as Monterey Jack or Oaxaca
2 tablespoons adobo sauce from a can of chipotle chiles in adobo, or your favorite hot sauce
1. Set the tenderloin pieces on a cutting board and rub them with 1 teaspoon of the salt and the pepper. Set aside.
2. Make the guasacaca: In the bowl of a food processor, add the avocados, onion, poblano chile, cilantro, jalapeño, garlic, vinegar, lime juice and the remaining 1 teaspoon salt. Process until smooth; then, with the machine running, add 2 tablespoons of the canola oil, processing until smooth.
3. Heat a large skillet (preferably cast iron) over medium-high heat until it smokes, about 2 minutes. Divide 1 tablespoon of the canola oil over the tenderloin pieces, rubbing it all over. Cook until all sides are browned and the internal temperature reads between 125° and 130°, about 10 to 12 minutes total. Transfer to a cutting board and rest the steak for 5 minutes, then slice crosswise into ¼-inch-thick pieces (about 16 slices total).
4. Set the cleaned skillet over medium heat and add 1½ teaspoons of the canola oil. Add a tortilla followed by ½ cup of cheese, 8 tenderloin slices and another ½ cup cheese. Place another tortilla on top. Cook until the tortilla is browned, 2 to 2½ minutes, then use a metal spatula to flip. Cook until the other side is browned, about 1½ to 2 minutes longer. Transfer the quesadilla to a clean cutting board. Repeat with the remaining ½ teaspoon of canola oil and the remaining tortillas, cheese and steak. Slice the quesadillas into quarters and serve topped with the guasacaca and a drizzle of adobo sauce.