In a large pot or Dutch oven, heat the vegetable oil over medium-high heat.
Add the beef, pork, and oxtail pieces to the pot in batches, searing them until browned on all sides. Remove the meat and set aside.
In the same pot, add the finely chopped onion, minced garlic, minced ginger, and chopped green onions. Sauté until the onions are translucent, about 5 minutes.
Return the seared meat to the pot.
Add the cassareep (or molasses), brown sugar, soy sauce, Worcestershire sauce, ground allspice, ground cinnamon, and ground cloves.
Pour in the water or beef broth and stir to combine.
Add the whole Scotch bonnet pepper if using, being careful not to break it open unless you want extra heat.
Bring the mixture to a boil, then reduce the heat to low.
Cover the pot and let it simmer for about 2-3 hours, or until the meat is tender and the flavors are well combined. Stir occasionally and add more water or broth if needed to keep the meat submerged.
Taste the pepperpot and adjust the seasoning with salt and black pepper as needed.
Remove the Scotch bonnet pepper before serving.
Ladle the pepperpot into bowls and garnish with fresh thyme sprigs if desired.
Enjoy your meal!