In a medium saucepan, bring the dashi to a gentle simmer over medium heat. Do not let it boil.
Place the miso paste in a small bowl.
Add a ladleful of hot dashi to the miso paste and whisk until smooth.
Return the miso mixture to the saucepan and stir gently to combine.
Add the tofu cubes to the soup and simmer for 2–3 minutes until heated through.
If using, add the wakame seaweed and nori strips and simmer for another 1–2 minutes.
Ladle the miso soup into bowls and garnish with sliced green onions. Serve hot.
Enjoy your meal!