Wash and drain dried shrimp, slice the onions finely, slice the garlic thick.
Soak tamarind in 1/2 cup of water, extract juice. Strain the juice if necessary, dissolve in the shrimp paste. Pound or grind the shrimp to powder (not too fine).
Heat oil in wok, add turmeric, brown the onions, drain off and set aside. Fry the garlic to a light brown, drain off and set aside. Into the hot oil put the powdered shrimp, fry until crisp but not dark, drain quickly.
Pour out oil and clean the wok. Return 2 tsp of oil to wok. Add the tamarind and shrimp paste liquid, a pinch of turmeric, and stir over fire.
As liquid reduces, add the chili powder and stir until chili powder darkens. Return shrimp and mix over fire for ~1 minute.
Add salt if needed, take off fire and cool. After cooled, mix in the onion and garlic.