Cold buttermilk soups are an old-fashioned tradition, a tangy zip for fresh, summer vegetables that need little else. Here, the sweet, grassy mellowness of cucumbers is paired with that summery perfume of basil, distilled into a finishing oil you can keep on hand to drizzle on future soups and salads. It's an irresistible, bright, almost ethereal combination that may well sum up the season. But we didn't stop there; We gave the pairing a tangy jolt with buttermilk and sour cream so that the flavors can't turn listless. If you've got weekend guests for a dinner party this evening, skip this one as a second or third course and consider serving it in shot glasses as a midday pick-me-up on the deck. — Vegetarian Dinner Parties
Prepare the basil oil up to 1 week in advance. Store, covered, in the fridge. If it hardens, run warm water over the container to loosen the oil.
Prepare the soup up to 1 day in advance.
To save time, use store-bought basil oil instead of making your own.
Look for real buttermilk, not the more common cultured substitute in our supermarkets. Real buttermilk — the liquid left over after making butter — will have a less sour, more savory finish, which will better match the cucumbers and basil.
For proper body and mouth feel, do not use "lite" or fat-free sour cream.
Reprinted from Vegetarian Dinner Parties by Bruce Weinstein & Mark Scarbrough. Copyright (c) 2014 by Bruce Weinstein and Mark Scarbrough. By permission of Rodale Books. Available wherever books are sold.
Peel the cucumbers, halve them lengthwise, and use a small spoon to scrape out (and discard) the seeds. Chop the cucumbers into small bits and add them to a large blender.
Add the celery, scallions, olive oil, basil, salt, and white pepper. Cover and blend until fairly smooth (there will be bits of celery string in the mix).
Strain the purée into a large bowl through a fine-mesh sieve or a colander lined with cheesecloth. Whisk in the buttermilk and sour cream. Cover and refrigerate for at least 4 hours.
Fill a large bowl with ice water. Bring a medium saucepan of water to a boil over high heat. Add the basil leaves to the hot water and once you see the first bubble after throwing them in, wait 10 seconds then remove and blanch the basil. Use a slotted spoon to transfer the leaves from the saucepan to the bowl with the ice water. Add more ice, chill for a few minutes, then skim the leaves out of the bowl with a slotted spoon and dry the leaves on paper towels.
Purée the basil with the olive oil in a blender. Let stand at room temperature for 1 hour to settle. Strain into a small bowl through a colander lined with cheesecloth.
To serve, ladle the soup into bowls. Drizzle each serving with basil oil.