April 8th, 2012
Purée buttermilk, yogurt, avocado, and a quarter of the peeled cucumber in a blender until smooth, then pour into a bowl.
Mash garlic with 1/2 teaspoon salt and stir it into the purée with green onions, herbs, chili, and lime zest. Season to taste with salt, pepper, lime juice.
Seed and finely dice remaining cucumber and add to soup. Cover and refrigerate if you're not eating immediately. Just before serving, taste and correct seasonings.
Ladle soup into bowls, then cover the surface with the chives, radishes, herb sprigs, and pistachios.