1. Soak tamarind in hot water for 1/2 hr, remove the fibrous threads while keeping the seeds, then squeeze the seeds in water, set aside.
2. Slice yellow and red bell pepper into strips; slice red onion; cut Chinese celery and scallion into sections; mince garlic, shallot and ginger, set aside.
3. Chop mud crab along the midline, snap the top off, remove the stomach and gills, chop off the claws, rinse and then chop the body into pieces, smash the claw with a blade.
4. Prepare tamarind sauce. Heat oil in a wok, sauté ginger, shallot and half of the garlic until fragrant, add tamarind seeds with the liquid, pour in 50ml of water. Add slab sugar, keep stirring until it melts, then season with chicken powder, salt and fish sauce, bring to a boil, then turn off heat and set aside.
5. Dust crab with corn starch, slide into boiling oil piece by piece; deep fry the claws first as they take longer to cook, the slide in the rest of the crab. Drain.
6. Heat another wok, drizzle in oil, sauté minced garlic, then add the deep fried crab, add 3 tbsp of tamarind sauce and a little water, mix well.
7. Season with pepper, salt, sugar and fish sauce, stir in Chinese celery, scallion, red onion, red and yellow bell peppers, mix well and serve.