Step 1: Pat the short ribs dry thoroughly with paper towels and season generously with salt and black pepper.
Step 2: Heat 2 tablespoons of olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat until shimmering. Sear the short ribs on all sides until deeply browned, about 3-4 minutes per side. Remove the ribs and set aside.
Step 3: Reduce heat to medium. Add sliced onions, ginger, and smashed garlic to the pot. Sauté until softened and fragrant, about 5-7 minutes. Add star anise, cinnamon stick, and cardamom pods. Toast for 1 minute until aromatic.
Step 4: Pour in beef broth and soy sauce, scraping up any browned bits from the bottom of the pot. Bring to a simmer.
Step 5: Return the short ribs to the pot, ensuring they are mostly submerged. Add the fish sauce and brown sugar. Bring back to a gentle simmer, then cover and transfer to a preheated oven at 325°F (160°C).
Step 6: Braise for 3-4 hours, or until the short ribs are fork-tender and easily pull apart. Check occasionally to ensure liquid levels are adequate. If the liquid reduces too much, add a little more beef broth.
Step 7: Once cooked, carefully remove the short ribs from the pot and set aside to cool slightly. Strain the braising liquid through a fine-mesh sieve into a separate saucepan. Discard solids. Skim off any excess fat from the surface of the strained liquid (the pho jus). Keep the jus warm over low heat.
Step 8: Shred the cooled short ribs using two forks, discarding any large pieces of fat or bone.
Step 9: For the Thai Basil Chimichurri: In a food processor, combine fresh Thai basil leaves, cilantro, mint leaves, garlic cloves, red chili, rice vinegar, lime juice, and fish sauce.
Step 10: Pulse until finely chopped but not puréed. Slowly drizzle in the extra virgin olive oil while pulsing until just combined. Season with a pinch of salt to taste. Set aside.
Step 11: Assemble the Banh Mi: Slice the banh mi baguettes or French bread horizontally, but not all the way through, creating a pocket. Lightly toast or warm them in a dry pan or oven until crispy on the outside and soft inside.
Step 12: Spread a generous layer of mayonnaise (or sriracha mayo for a kick) on the inside of both halves of the bread.
Step 13: Fill the bread with a generous amount of shredded short ribs.
Step 14: Top the short ribs with pickled daikon and carrots, cucumber slices, and fresh jalapeño slices (if using).
Step 15: Drizzle a generous spoonful of the Thai basil chimichurri over the fillings.
Step 16: Close the sandwich. Serve immediately with small bowls of the warm pho jus for dipping.