Clean the shrimp, peel and devein them, and remove the heads if you prefer.

Peel and clean the green papaya, cut it into bite-sized pieces, rinse off the sap in water, and soak it for a bit.

Dissolve the tamarind pulp in warm water. If you prefer, you can microwave the tamarind with water to soften it, then mash to extract the juice.

Remove the bones from the mackerel and flake the meat. Pound the mackerel meat together with the gaeng som curry paste in a mortar and pestle until well combined.

Add the mackerel and curry paste mixture to a pot and dissolve it in water.

Season the soup with the tamarind juice, sugar, fish sauce, and seasoning powder. Taste and adjust the flavor as you like.

Add the green papaya to the soup and simmer until it reaches your desired tenderness.

Taste again. If the flavor is good, add the shrimp and cook until just done. If you want it more sour, turn off the heat and add a squeeze of lime juice for extra tanginess. Now you have gaeng som.

Serve hot with steamed rice. The thick, flavorful soup with mackerel gets even better when reheated.