an 8- to 10-quart stovetop pressure cooker; a squeeze bottle
For the oxtail braise: Heat the olive oil in an 8- to 10-quart stovetop pressure cooker. Meanwhile, sprinkle the oxtails generously with salt and pepper and add to the oil. Sear the oxtails on both sides, about 5 minutes per side. Add the onions, carrots, celery, guajillo chiles, garlic, tarragon, thyme, parsley, black peppercorns, avocado leaves, bone broth, Mexican cola and demi-glace. Lock on the pressure cooker lid and pressure cook at high pressure for 30 minutes. Carefully quick-release the pressure, then unlock the lid and open.
Place the oxtails in a shallow dish. Strain the liquid from the pressure cooker and pour into a medium saucepan. Put over medium-high heat and bring to a boil. Meanwhile, once the oxtails are just cool enough to handle, carefully remove the meat from the bone and shred. Add the shredded oxtail to the sauce and stir to combine. Taste and adjust the seasoning with salt. Just before serving, stir in the cilantro.
For the quick pickled red onion and Fresno: Add the red onion, Fresno and salt to a small bowl. Pour the apple cider vinegar over the top and allow to sit and quick-pickle while you get the rest of the toppings ready. Drain prior to serving.
For the crema: Add the avocado flesh, lime juice, sour cream, milk, salt and cilantro to a blender and blend until combined. Pour into a squeeze bottle and set aside until ready to serve.
For serving: Preheat a fryer or a large Dutch oven filled with 3 inches of oil to 350 degrees F. Line a sheet tray with a wire rack.
Add the corn tortillas to the heated oil and fry until golden brown on both sides, about 1 minute per side. Drain on the wire rack. Season with salt.
Combine the green and red cabbage in a bowl and toss until just combined.
Place the tostadas on a plate. Top with a generous amount of avocado crema, oxtail with sauce, cabbages, pickled onions and Fresno, sliced radishes and freshly grated Cotija. Serve with the lime wedges.