Sear the oxtails: Heat the olive oil in a large braiser or dutch oven over medium-high heat. Season the oxtails with salt and pepper, and sear them on all sides until browned. You may need to do this in batches. Transfer the oxtails to a plate and set the oxtails aside.

Sauté: Add the onion to the pot and cook until translucent and softened, 3-5 minutes. Add the garlic, ginger and habanero, then stir and cook for 1 minute. Stir in the allspice, smoked paprika, soy sauce, tomato paste, and cook for 2-3 minutes until the paste browns slightly.

Braise: Add the oxtails back to the pot. Stir in the beef broth, thyme, bay leaves and bring the pot to a boil. You want to have enough broth to cover most of the oxtails, so start with 4 cups and add more as necessary. Turn the heat to low and cover with a lid slightly cracked. Simmer for 2 hours, remove the lid and stir in the butter beans, then simmer for another 30-45 minutes uncovered.

Finish: Remove the bay leaves and thyme sprigs. Whisk the cornstarch with 1 tbsp water to create a slurry. Stir the slurry into the pot and increase the heat to medium, stirring until the mixture thickens. Garnish with freshly chopped green onion.