Clean the crab and chop it into smaller pieces. Season them with soup powder, brown sugar, and red pepper powder. Mix well and let the crab sit for 15 minutes.
Mince lemongrass, garlic, and shallots. Next, finely chop the laksa leaves and thinly slice the ginger.
Soak the sour tamarind in warm water, and press them with a spoon to release the flavor. Whisk the tapioca flour in cool water.
Heat a pan on the stovetop and roast the peanuts for 5 minutes or until golden brown. Wait for them to cool and remove the skin.
Add some oil to the pan. Roll the crab meat through the crispy flour. Once the oil is heated, fry the crab for about 5 minutes until all sides are cooked. Set aside.
Add a little oil to a clean, heated pan and fry the minced lemongrass until fragrant. Add the shallots, garlic, and ginger to the pan and stir for 2 to 3 minutes. When the herbs and spices turn aromatic, add the tamarind water. Stir and season the mixture with oyster sauce, chili sauce, fish sauce, and brown sugar. Put the fried crab in the pan and stir for 2 to 3 minutes. Add the chopped laksa leaves and continue stirring for another 5 minutes. Lastly, pour in the tapioca flour-water mixture and stir until the sauce is slightly thickened. Enjoy while the dish is hot.