Sear lamb in hot oil until browned all over. Set aside.
Fry massaman paste in the same pot 2 minutes.
Add coconut milk, stock, cinnamon, cardamom, star anise, and bay leaves.
Return the lamb. Bring to a simmer, cover, and cook 1.5–2 hours until very tender.
Add tamarind, fish sauce, and erythritol. Adjust seasoning.
Stir in peanuts or almonds and cook 5 more minutes.
Serve garnished with fried shallots and more peanuts.