Original source: Epicurious.com, but I didn’t blend it
2 scallions, minced
1 small garlic clove, minced
1/4 teaspoon minced small fresh hot green chile such as serrano or Thai, or to taste
1/2 tablespoon unsalted butter
1 1/2 lb chayotes* (2 to 3), peeled, quartered lengthwise, and pitted if necessary, then cut into 1/2-inch pieces (4 cups)
1/2 teaspoon salt
2 tablespoons finely chopped fresh cilantro
1 3/4 cups water
Cook scallions, garlic, and chile in butter in a 3-quart heavy saucepan over moderately low heat, stirring, until softened, about 3 minutes. Add chayotes, salt, and 1 tablespoon cilantro and cook, stirring, 2 minutes. Add water and simmer, covered, until chayotes are very tender, 15 to 20 minutes.
Stir in remaining tablespoon cilantro and purée soup in 2 batches in a blender until smooth (use caution when blending hot liquids). Season with salt.