Here's the recipe I like to use:
* 2 teaspoons dashi granules
* 4 cups water
* 3 tablespoons miso paste
* 1 (8 ounce) package silken tofu, diced
* 2 green onions, sliced diagonally into 1/2 inch pieces
In a medium saucepan over medium-high heat, combine dashi granules and water; bring to a boil. Reduce heat to medium, and whisk in the miso paste. Stir in tofu. Separate the layers of the green onions, and add them to the soup. Simmer gently for 2 to 3 minutes before serving.
Dashi is a combination of seaweed and fish. Alternatively, you can use a dashi soup stock to start. Yellow miso paste is sweet and creamy, red miso is stronger and saltier.