Bring a large pot of water to a boil and add the beets. Reduce the heat and simmer uncovered for 35 to 40 minutes or until the beets are tender when pierced with a knife. Drain and allow them to cool enough to handle. Peel and cut them into chunks and set aside.

Heat the oil in a small skillet over medium heat, add the onion, salt and pepper to taste and cook until tender and barely golden, 5 to 7 minutes. Add the garlic and cook for 2 minutes longer.

Put the onion mixture and the beets in a blender. Add 2-1/2 cups of the vegetable stock and puree until smooth. Add the orange juice, lemon juice, white wine vinegar, salt, and a few grinds of black pepper. Add more stock if necessary to achieve the desired consistency. Taste and adjust seasoning.

Chill the soup thoroughly - several hours is best. Before serving, ladle the soup into individual serving bowls. Garnish each with about 2 teaspoons of sour cream and a sprinkling of fresh chopped dill.