Gather all ingredients and have them measured and prepared before starting.

In a medium saucepan, bring water to a gentle simmer over medium heat. (If using prepared dashi instead of water and granules, simply heat the dashi.)

Add dashi granules to the water and stir until completely dissolved.

Reduce heat to low to maintain a gentle simmer. Do not boil once the dashi is ready.

Place miso paste in a small bowl. Ladle about 1/2 cup of the hot dashi broth into the bowl and whisk until the miso is completely dissolved with no lumps.

Pour the miso mixture back into the pot and stir gently to combine.

Add the cubed tofu and any optional ingredients like seaweed or mushrooms. Warm for 1-2 minutes.

Remove from heat and garnish with sliced green onions before serving.