Peel the cucumber and slice in half lengthwise. Scoop out the seeds and slice into chunks. In a blender, puree the cucumber, celery stalks, shallot, 1/4 cup olive oil and 1 teaspoon kosher salt until smooth. Strain through a medium-mesh sieve into a large bowl, pressing on the solids to extract as much liquid as possible.

​Whisk in the cour cream and buttermilk then season to taste with salt and black pepper.

​Refrigerate until chilled, at least 1 hour.

​Serve drizzled with extra-virgin olive oil and garnished with chopped chives.

​Note: You can make this no cook soup up to 2 days ahead.