Preheat the oven to 350°F with a rack in the center position.

Season the beef all over with the salt and pepper. Heat the olive oil in a Dutch oven over medium-high heat. Once the oil is glistening, add the meat and cook until browned all over, about 5 minutes per side. Transfer the beef to a plate.

Set aside 1 cup of the coconut milk for later use. To the Dutch oven, add the remaining coconut milk, 1 cup of the beef stock, the red curry paste, lime zest, lime juice, onion, garlic, lemongrass, and ginger. Whisk to combine. Bring the mixture to a simmer, then return the meat to the pot along with any collected juices, nestling it into the liquid. Cover the pot and transfer it to the oven. Cook for about 2-2½ hours, or until the meat is very tender.

Using tongs or two forks, transfer the meat to a plate and shred it, discarding any large pieces of fat. Return the shredded beef to the curry and stir to incorporate. Set the pot over high heat.

Add the remaining 1 cup beef stock, reserved 1 cup coconut milk, sweet potato, and bell pepper. Bring to a boil, then reduce the heat to medium-low and cook, simmering, until the sweet potato is tender, about 20 minutes.

Serve the curry and vegetables spooned over the cooked rice if using. Top with cilantro, Thai basil, and Thai chilies if desired.