In a medium pot, heat the oil over medium heat. Sauté the onions and garlic until soft and light brown, 4 to 5 minutes. Add the beets, bay leaves, carrots, and stock and bring to a boil. Reduce the heat and simmer for 35 to 40 minutes, until the beets are soft. Remove the bay leaves. Transfer the soup to a blender, in batches if necessary, and puree until smooth.
Return the soup to the pot and reheat. Season with the chili powder, lemon juice, and salt and pepper.
Pour the soup into bowls. Add a tablespoon of sour cream to each bowl, and serve.