Heat a generous splash of vegetable oil in a large oven-safe pan over medium heat. Add the sliced onion and sauté for 5-7 minutes until it becomes softened and translucent. Stir in the Massaman curry paste along with 1/2 cup of coconut milk, cooking until fragrant and the mixture brightens in color, about 2 minutes.

Once the aromatics are ready, add the rest of the coconut milk, water, and the beef short ribs to the pan. Stir gently to combine the ingredients, ensuring the beef is well coated with the flavorful sauce. Cover the pan and place it in a preheated oven at 160°C (325°F) for 2 hours.

After 2 hours, carefully check the short ribs; they should easily pull away from the bone. Remove any bones if necessary, then add the quartered potatoes to the curry. Cover the pan again, and return it to the oven for an additional 30 minutes.

Once the potatoes are tender, remove the pan from the oven and stir in the tamarind paste, brown sugar, and roasted peanuts. Return the pan to the oven uncovered and let it cook for an extra 20-30 minutes.

When the beef is fork-tender, use two forks to shred the meat and mix it back into the sauce for a cohesive dish. Serve hot over jasmine rice or alongside naan.