Saute onion, carrots and garlic over medium heat. 7 minutes. add stock, kombu, half of scallions and daikon. Bring to simmer, 5 minutes. add udon. cook over medium heat until noodles are al dente. Meanwhile, dissolve miso paste in 3 tablespoons warm water. just before serving, stir in paste. do not boil soup once miso has been added. ladle soup in bowls and top with scallions and bean sprouts. season with salt and pepper at table.