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1
Place raw peanuts in a dry pan over moderate heat and roast, stirring frequently, until they reach a deep gold — deeper than a garnish roast, with a developed, slightly bitter-caramel note — because that bitterness is what keeps the finished sauce from tasting flat and sweet once the coconut milk and sugar are in. Remove and allow to cool. Grind in a food processor or mortar to a rough paste, stopping when no whole peanuts remain but the mass is still coarse and irregular, so the sauce retains body and chew rather than dissolving into smoothness.
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2
Place the coconut cream in a wok or saucepan over medium heat and cook until it cracks — the fat separates, the surface shimmers and pools — because the freed fat is what carries and toasts the curry paste rather than simply boiling it. Add the red curry paste and fry for 2 minutes, stirring it constantly into the cracked cream until it smells aromatic and cooked rather than raw.
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3
Add the ground roasted peanut paste to the fried curry paste and stir until fully combined, then pour in the thin coconut milk so the peanut paste loosens gradually and does not seize into lumps. Simmer gently for 5 minutes, stirring to prevent the peanut from catching on the base, until the sauce has cohered into a single body and the raw coconut milk smell has cooked off.
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4
This is where the dish lives or dies. Add the tamarind water, palm sugar, and fish sauce, then taste and adjust each element in turn against the others, because the four notes — the peanut's roasted-fat richness, the curry paste's aromatic heat, the sweet-sour of palm sugar and tamarind, and the fish sauce's savoury background — must arrive in that sequence on the palate simultaneously rather than any one riding over the rest. A sauce that reads only as rich and sweet is under-acidified; add more tamarind until the tartness just cuts through the richness without announcing itself.
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5
Check consistency by lifting a spoon from the sauce and tilting it: the sauce should coat the back and flow slowly, not run, so it will cling to a piece of satay rather than sliding straight off. If too thin, continue simmering to reduce; if too thick, add coconut milk in small increments until the texture is cloaking but still pourable.