1. In a large pot, bring broth to a simmer over medium heat. Remove 1/2 cup to a small bowl and whisk in miso until dissolved.
2. Add carrots, mushrooms and corn to pot and cook, stirring occasionally, for 3 minutes. Add snow peas, spinach and scallions; cook for 1 minute. Stir in miso mixture. Simmer for 5 minutes, lowering heat if necessary to prevent boiling. Stir in tofu and cook until heated through, about 1 minute. Ladle into bowls and serve.