"Living in San Francisco, I've had more than my fair share of crab, prepared in more ways than I can remember. I've never enjoyed it more than in this Singapore-style chili crabs recipe. Just be sure to have lots of napkins around. My friends in Singapore tell me they serve this with at least twice the amount of sauce, and a type of fried roll to soak up the goodness with. So, if you want to rock the chili crab like a Singaporean, then you should probably double the sauce ingredients!"
Whisk ketchup, chicken broth, egg, soy sauce, chile-garlic sauce, oyster sauce, tamarind paste, fish sauce, and palm sugar together in a bowl.
Stir shallots, garlic, oil, ginger, and serrano pepper together in a pot over medium-high heat. Saute until sizzling, about 2 minutes. Add crab to pot, cover the pot with a lid, and shake until crab is completely coated in shallot mixture. Remove lid and cook and stir until heated through, about 3 minutes.
Pour ketchup mixture into pot, reduce heat to medium, and cook and stir until sauce thickens and crab is hot about 5 minutes. Remove from heat; stir in cilantro and green onions.