In a large pot over medium heat, soften the onion in the butter for 5 minutes. Add the carrots, garlic and couscous. Cook, stirring, for 2 minutes. Season with salt and pepper. Add the broth and carrot juice and bring to a boil. Cover and simmer for 20 minutes over low heat or until the couscous is al dente (see note). Add the spinach, cream and cheese. Stir well and adjust the seasoning.