Heat the vegetable oil in a large pot or Dutch oven over medium-high heat.
Add the beef, chicken, or lamb pieces and cook until browned on all sides. Remove and set aside.
In the same pot, add the sliced onion and minced garlic. Sauté until the onion is soft and translucent, about 5 minutes.
Add the Massaman curry paste to the pot and stir-fry for 1-2 minutes until fragrant.
Pour in the coconut milk and bring to a simmer.
Add the cinnamon stick and bay leaves.
Add the cubed potatoes and sliced carrots to the pot.
Return the browned meat to the pot as well.
Stir in the fish sauce, tamarind paste, brown sugar, and roasted peanuts.
Add the water or chicken broth to reach your desired consistency.
Reduce the heat to low and let the curry simmer for about 30-40 minutes, or until the meat and vegetables are tender.
Remove the cinnamon stick and bay leaves before serving.
Enjoy your meal!