Don’t overcook the spinach or it will lose its bright green color.
Combine stock, onion, cucumbers, carrots, bay leaf, and summer savory in soup kettle. Simmer, partially covered, 15 minutes over low heat. In separate saucepan boil potato 15 minutes or until tender. In another pan boil or steam spinach for several minutes. Remove bay leaf from vegetables in kettle. Combine drained potato and drained spinach with other vegetables and press through food mill. Season with salt and pepper. Cool, chill, and stir in sour cream. Serve cold, garnished with chopped cucumber.