Wake up the paste: heat the thick coconut cream from the top of the can in a large Dutch oven or heavy pot over medium-high heat. Add the massaman curry paste and coconut oil; fry 2-3 minutes, pressing the paste against the hot surface, until deeply fragrant and a shade darker.
Start the beef: add the beef chunks and stir to coat in the paste. Pour in the remaining coconut milk, broth, tamarind, palm sugar, fish sauce, peanuts, cinnamon stick, cardamom pods, and bay leaves. Bring to a gentle simmer, cover, and bubble softly for 45 minutes, stirring once or twice.
Add the potatoes and onion: stir in the potato chunks and onion wedges, keeping them mostly submerged. Cover and simmer 25-30 minutes more, until the potatoes are fork-tender and the beef is silky and tender. Add a splash of broth or water if the sauce reduces too much.
Rest and balance: take off the heat and rest, covered, for 10 minutes. Fish out the cinnamon stick and large cardamom pieces. Taste and adjust fish sauce, sugar, and tamarind until rich and rounded with a gentle sour note in the background.
Serve: ladle over hot jasmine rice and scatter with fresh cilantro and crushed peanuts.