Season the oxtail with salt. Heat the lard in a large Dutch oven, over medium-high heat, until shimmering. Add the oxtail pieces in a single layer, without overcrowding the pot. Sear the meat, turning occasionally, until brown on all sides, about 8 minutes total. Remove the oxtail pieces and reserve.

Lower the heat to medium and add the onion and garlic. Cook until fragrant and softened, about 3 minutes. Add the tomatoes and stir to combine. Pour the beef broth and the bay leaves. Bring to a boil, scrapping the browned bits from the bottom of the pan.

Return oxtail to the pot. Cover, lower the heat to a simmer, and cook for 2 to 3 hours or until the meat is falling apart tender. Remove the oxtail pieces and shred the meat, discarding the bones and any large pieces of fat if desired. Cover and refrigerate for 1 hour or until chilled and can easily form into a patty (you can freeze for 30 minutes to speed up the chilling).

Bring the remaining sauce in the pot to a boil to reduce, over medium high heat, for about 15 minutes or until reduced by half. Remove the bay leaves. Spoon off fat from surface of pan juices and discard. Taste and add salt if desired.

Remove the oxtail from the fridge or freezer, form into a tightly compacted 1/2 pound patty (resembling a hamburger). Heat the duck fat in a large skillet over medium high heat. Once hot, add the oxtail patty and fry for 1 minute, flip and cook another minute or until outside is crispy. Remove with a spatula and place into a wide soup bowl.

Just before serving, pour 1/2 cup of the rendered stock from the pot. Garnish with a Boston lettuce leaf and fill with fresh herbs if desired. Serve fresh.