In a medium saucepan, heat the olive oil over medium heat. Add the carrots and the onion and sweat until the mixture starts to soften, about 5 minutes. Add the garlic, orange zest and oregano and cook until fragrant, another 1 to 2 minutes. Raise the heat and deglaze the pan with white wine. Add the stock and water. Bring to a boil and reduce to a simmer. Cook until the carrots are tender, about 8 to 10 minutes. Cool the mixture for about 5 minutes before processing.
Process the soup in a food processor or blender until smooth. Season with salt and pepper, to taste. Pour into serving bowls and swirl in a heaping teaspoon of sour cream before serving.