In a medium sauce pan over medium heat, melt the butter. Add the garlic, onions, celery, and leeks. Sauté for 4 to 5 minutes, stirring occasionally. Do not brown. When vegetables are slightly softened and translucent, add the potatoes, water, and bouillon. Simmer until the potatoes are soft. Remove from the heat and puree the soup using a blender or food processor. Return to pan, but do not heat. Season to taste with salt and pepper. Place the sour cream and milk into a small mixing bowl and temper this mixture into the soup by stirring a small amount of hot soup at a time into the cream mixture until it becomes warm. Then stir it back into the hot soup. Do not return to the heat. Warm soup when ready to serve, garnish with sliced scallions and a dollop of sour cream.

Serving suggestion: Can be served hot or cold for lunch or as an appetizer.