For sweet chilli sauce, combine water, chilli flakes, chilli and palm sugar in a small saucepan and stir over medium heat until sugar dissolves. Bring to the boil and simmer for 5-6 minutes, until mixture is reduced and thickened slightly. Season to taste with lime juice and fish sauce. Place in a small jug.
For chilli crab, heat peanut oil in a large frying pan over medium heat.
Sauté chilli, ginger and garlic for 1-2 minutes. Add fish sauce, tomato puree, sugar, stock, water and seasoning. Stir until the mixture boils.
Crack crab claws to allow the sauce to penetrate into the crab meat and cook in the sauce for about four minutes. Remove from pan once the shell colour changes to a bright orange. Keep warm.
Place half bodies and top shell in the pan and cook for five minutes, remove and keep warm.
Assemble the crab so it resembles its whole form. Serve with steamed rice and sweet chilli sauce. Garnish with coriander.