Heat 3 tablespoons of the oil in a large saucepan. Add the onion and cook for about 5 minutes, until soft. Add the remaining ingredients, except the salt and pepper, and the lemon juice. Bring to a boil. Lower the heat and simmer for 1 hour. Remove from stove and remove the bay leaf. Purée all the ingredients in a food processor or blender. Return pureed mixture to pan. Warm soup over low heat for 5 minutes or until thoroughly heated. Stir in 1 tablespoons of the lemon juice, ½ teaspoon of salt and 1 teaspoon of black pepper. Combine 1/2 cup soup with the sour cream, stirring with a whisk. Divide soup evenly among each of 8 bowls. For added creaminess and a lovely presentation, we swirled this vibrantly colored beet soup with sour cream. The bisque can be served hot or cold.