Make the stock: Heat 1 tbsp of oil in a pot over medium-high heat. Add the 2 cups of prawn heads and shells, sautéing for 5–10 minutes. Crush them with your spatula to release the juices.
Strain the broth into a clean bowl, discarding the shells, and set the prawn stock aside.
Blend the spice paste (rempah): Place all the Spice Paste ingredients into a food processor or heavy blender.Add 2 tbsp of water (only if needed to help the blades move) and blend into a very fine, uniform paste
Cook the gravy: Heat the remaining 3 tbsp of oil in a large pot over low-medium heat. Add the blended spice paste and stir-fry continuously for 15–20 minutes. The paste is ready when it darkens and the oil splits/separates
Pour in the strained prawn stock and bring to a simmer.
Stir in the 1 ¾ cups of coconut milk, 2 tbsp of fish sauce, and 1 tbsp of palm sugar. Toss in the halved tofu puffs so they absorb the liquid. Let it come to a gentle boil.
Blanch the thick rice vermicelli noodles and 1 cup of bean sprouts in a separate pot of boiling water for 1–2 minutes, then drain well.
Assemble and Serve: Divide the blanched noodles, and raw bean sprouts into 4 deep serving bowls.
Arrange the blanched prawns, fish cake slices, raw cockles, and tofu puffs, on top.
Ladle the piping hot laksa gravy over the ingredients.
Garnish generously with the 2 tbsp of finely chopped polygonum leaves leaves