In a blender, puree the chopped cucumbers with the chopped pepperoncini, the pickling liquid, 2 tablespoons of the dill, the yogurt and buttermilk until very smooth. Stir in the cumin and the remaining dill and season with salt. Refrigerate until chilled, about 30 minutes.
Ladle the soup into 6 bowls. Serve each bowl with a whole pepperoncini and cucumber spears on the side.