Melt butter in a large pot over medium heat and cook carrots, onions, and ginger until softened, about 5 minutes. Dust with flour and cook and stir for 2 minutes. Add broth, cover, and simmer until carrots are soft, 15 to 20 minutes. Season with sea salt and white pepper.
Puree carrot soup with an immersion blender until smooth.
Zest 1 orange until you get about 1 teaspoon zest. Juice both oranges.
Stir orange juice and creme fraiche into the soup and heat over medium-low heat, but do not boil. Stir in orange zest and season with salt and pepper. Sprinkle with pistachios.