Place all the curry paste ingredients in a food processor and blend until it forms a smooth mixture. Set aside.
Heat the oil in a large wok. Toss the chopped beef in the cornflour, salt and pepper.
Fry the beef chunks in hot oil for 5 mins on medium high heat until the exterior is browned.
Once the beef has cooked, turn down the heat to medium low and add in the curry paste. Stir to coat the beef and let it cook for an additional 2-3 minutes.
Add the beef stock and coconut milk. Stir and then cover with a lid while gently simmering on low heat for 1 hour 45 mins. Stir every so often and if the beef is starting to look dry add additional beef stock.
After the 1 hour 45 mins, add in the sweet potatoes, give it a stir and cook for a further 25 - 30 mins until the potatoes are tender. This is the perfect time to start cooking your rice!
Once Thai Beef & Sweet Potato Curry is fully cooked remove from the heat and add lime juice, tamarind paste and brown sugar.
Serve the Gaeng Masaman Curry with steamed rice topped with cilantro, chilies, wedge of lime, peanuts, lime leaf and fried onions.