Asian-style watermelon and crab soup

5 cups coarsely chopped seeded watermelon (preferably the Asian variety that has yellow skin, pink flesh and is very sweet)
1 fresh lemongrass stalk
3 tablespoons finely chopped shallot
1 1/2 tablespoons finely chopped peeled fresh galangal (substitute ginger)
1 tablespoon finely chopped garlic
1 1/2 tablespoons olive oil
1 small hot red Thai chile, chopped with seeds
fresh lime juice, to taste
salt, to taste

2 cups cooked and lumped crabmeat
1/4 cup fresh cilantro, chopped
1 1/2 tablespoons olive oil
salt, to taste

Purée watermelon in a blender until smooth and transfer to a bowl. (Don't wash blender.) Peel tough outer leaves of lemongrass stalk and thinly slice lower 5 to 6 inches, then mince. Cook lemongrass, shallot, ginger, and garlic in oil until everything is pale golden. Add about one third of watermelon purée and simmer over moderate heat for 5 minutes. Remove watermelon mixture from heat, then transfer to blender along with chile, lime juice, and salt and blend until smooth. Add remaining watermelon purée and blend briefly. Season soup with more chile, lime juice, and salt if desired, blending if necessary. Chill soup, uncovered, about 2 hours if serving cold, or reheat in cleaned saucepan.

Toss crabmeat with cilantro, oil, and salt. Mound the crab mixture in the centre of bowls and pour chilled or hot soup around it. Garnish with fresh lime wedges.

Served with coconut rice balls.