Toast the coriander seed, cumin seed, cinnamon, cardamom pods, cloves and star anise in a dry skillet over medium-low heat, shaking constantly, until the kitchen smells of warm spice and the seeds darken a shade, about 3 minutes. Tip onto a plate immediately so they stop cooking. Let cool, then grind to a fine powder along with the grated nutmeg.

Drain the soaked chillies and squeeze out the water. Pound them in the mortar with the salt until broken down into a rough red mash, about 5 minutes.

Add the lemongrass and galangal and pound until fibrous strands disappear. Work in the shallots, garlic, makrut lime zest and coriander roots one at a time, pounding each to a paste before adding the next. Finally pound in the shrimp paste and the ground toasted spices. You want a thick, smooth, deep red-brown paste. This takes 20 to 25 minutes by hand.

Open the cans of coconut milk without shaking them and spoon the thick cream from the top into a measuring cup. Reserve the thin milk below.

Heat the coconut cream plus the thick cream you skimmed in the heavy pot over medium heat. Let it bubble and reduce, stirring now and then, until it splits and clear coconut oil pools at the edges, 8 to 12 minutes. This is cracking the cream and it is the step that makes the dish.

Add the curry paste to the cracked cream and fry, stirring almost constantly, until the paste darkens and the oil separates out around it again, 6 to 8 minutes. It should smell sweet, toasty and deeply aromatic rather than raw.

Add the beef chunks and turn them in the paste until every piece is coated and the surfaces have taken on colour, about 5 minutes.

Pour in the reserved thin coconut milk and the water. Bring to a bare simmer, then lower the heat so the surface barely trembles. Partially cover and cook for 1 hour 30 minutes, stirring every 20 minutes or so, until the beef gives easily to a spoon.

Add the potatoes, onion wedges and peanuts. Simmer uncovered for 30 to 40 minutes, until the potatoes are tender all the way through and the sauce has thickened enough to coat a spoon.

Stir in the tamarind paste, palm sugar and fish sauce. Simmer 5 minutes more, then taste. It should land sweet first, then salty, with a clean sour note at the back and only a whisper of heat. Adjust with more palm sugar, fish sauce or tamarind until those three pull against each other evenly.

Take the pot off the heat and let the curry rest 15 minutes before serving. The oil will rise to the surface in a glossy reddish slick, which is exactly what you want.