Spice Paste (Kreung)
Process all ingredients for the spice paste in a food processor or coffee grinder until well ground. It should form a moist paste, somewhat similar to Thai curry paste.
Coconut Sauce (Amok) and Fish (Trei)
Mix together the processed spice paste with the fish sauce, palm sugar, mushroom seasoning, salt, and shrimp paste in a medium bowl.
Add coconut milk and beaten egg yolk to the mixture and stir until well combined.
Add cubed fish and stir.