If using the miso-infused broth, combine 1 tablespoon miso with 4 1/2 cups water and bring to a boil. Reduce the heat and simmer.
In a large saucepan, heat the olive oil over medium-high heat. Add the rice, stirring constantly
in one direction, until well coated. Remove the pan from the heat and add the sake. Return to the heat and stir constantly in one direction until all of the liquid is absorbed.
Add the stock or broth in 1/2-cup increments, stirring constantly until the liquid is absorbed with each addition. Season with salt and pepper.
Spoon into serving bowls, garnish with the mushrooms, scallions, and sprouts and serve.