In a large mixing bowl, combine the boneless top sirloin roast with beef bouillon, chopped onion, black pepper, minced garlic, and whole scotch bonnet pepper. Mix well to coat the meat evenly. Cover and refrigerate for at least 4 hours or overnight.

Remove the marinated beef from the refrigerator 30 minutes before cooking to allow even cooking.

In a heavy-duty pot or Dutch oven, heat 2 tablespoons of vegetable oil over medium-high heat. Carefully add the roast, searing for about 4-5 minutes on each side until a deep brown crust forms. Remove the meat and set it aside on a plate.

Using the same pot, add chopped carrots, celery, and any remaining onion. Sauté for about 5 minutes until softened.

Pour in 2 cups of beef broth, scraping the bottom of the pot to deglaze.

Return the seared beef to the pot, ensuring it sits snugly among the vegetables. Add enough broth to cover about one-third of the roast height. Simmer, cover, and reduce heat to low, cooking for 2.5 to 3 hours.

When the beef is nearly tender, around the 2-hour mark, add the skin-on baby potatoes to the pot.

Once the beef is fall-apart tender, remove it from the pot and let it rest for 10 minutes before slicing. Serve hot with gravy.