Remove Shell and de-vein shrimps.
Marinade the shrimp with 2 Tbsp of soy sauce for 10 minutes.
Mean while, thinly slice sweet peppers and steam pea pods, these will be used as sides.
Finely Chop up shallot onion, mince garlic, and thinly chop scallion. Keep the white part separate from the greens.
Microwave half cup of water until hot enough, add the tamarind paste and mill it with enough pressure so that all the flesh are smashed and dissolved into liquid. If you're using raw whole tamarind, after smashing, remove the side fiber and seeds.
Strain through a fine mesh while smashing the flesh to get all the juice and flavor out.
Add 3 Tbsp sugar to the tamarind juice, stir to mix and dissolve.
In another container, mix 2 Tbsp cornstarch with 2 Tbsp of water and 1 tsp sesame oil, set aside.
Using a wok or large saute pan over high heat, add 2 Tbsp of oil. Swirl the oil out to evenly coat the saute pan.
When oil is hot, add minced garlic and 1/2 tsp annatto powder, quickly stir till golden and giving off aroma.
Add the shrimp to saute pan along with the marinade soy sauce, keep stirring to let them cook evenly for about 2 - 3 minutes, just until they're lightly done but not cooked all of the way. Quickly remove the shrimp to a plate.
Using the same saute pan/wok, add chopped shallot onion and chopped white part of scallion. Stirring until they are soften enough and starting to be more translucent.
Pour in the prepared tamarind mixture and 1 cup of unsalted chicken stock. Wait until the mixture is boil rigorously. This will reduce the amount of liquid and thicken the sauce a bit. Adjust this sauce to taste so that it is sweet & sour if need.
Now add back the shrimp into the boiling sauce, stir to let the shrimp fully coated with sauce.
Stir the cornstarch mixture so that leaving no residue on bottom while pouring this mixture into the sauce pan.
Keep stirring and whirling to let everything mix, the sauce will become thicker every second and create beautiful coat around every shrimp.
When the shrimps are done (do not over cook) and evenly coated, turn off heat.
Add chopped green scallion and sprinkle on some ground pepper, stir to mix them.
Served over bedded rice, sweet pepper and steam pea pods as sides. Topped with some roasted sesame seeds.