Step 1

Peel, seed, and chop 2 of the cucumbers. Thinly slice remaining cucumber to equal 1/4 cup rounds. (Discard remaining cucumber, or reserve for another use.) Process chopped cucumbers, buttermilk, yogurt, mint, tarragon, lemon zest and juice, and salt in a blender until very smooth, about 2 minutes, stopping to scrape down sides as needed. Chill 1 hour.

Step 2

To serve, top with a swirl of buttermilk, and garnish with diced cucumber and fresh tarragon leaves.