Thai-Spiced Watermelon Soup With Crabmeat

Ingredients

• 5 cups coarsely chopped seeded watermelon (from a 4-lb piece, rind discarded)
• 1 fresh lemongrass stalk*
• 3 tablespoons finely chopped shallot
• 1 1/2 tablespoons finely chopped peeled fresh ginger
• 1 tablespoon finely chopped garlic
• 1 1/2 tablespoons mild olive oil
• 1 small hot green chile such as thai or serrano, finely chopped (including seeds), or to taste
• 2 tablespoons fresh lime juice, or to taste
• 3/4 teaspoon salt, or to taste
• 10 oz jumbo lump crabmeat (2 cups), picked over
• 1/4 cup finely chopped fresh cilantro
• 1 1/2 tablespoons mild olive oil
• 1/4 teaspoon salt, or to taste