Prepare the rice: Wash the rice to remove any dust or debris. Drain and repeat two or three times. Soak the rice in cold water for 30 minutes.

Season the water: In a container, combine 2 cups of water with the soy sauce, mirin, and chicken bouillon powder. Mix well and set aside.

Prepare the vegetables: Finely chop the garlic cloves. Thinly slice the green onions, separating the whites and greens. Quarter the mushrooms (if using) and cut the potatoes into bite-sized cubes.

Optional sauce for one-pot rice: In a small container, combine all the sauce ingredients and mix well. Set aside.

Heat the oil over medium-high heat. Once it gets nice and hot, add the ground beef, spread it out, and season with a pinch of salt. Sear for 2 minutes or until the bottom is golden brown. Flip, break up the beef, and cook for 1 more minute.

Add the garlic, white parts of the green onions, mushrooms, and potatoes. Sauté for 4 to 5 minutes, or until the potatoes start to soften.

Add the drained rice and stir for 1 minute to help the grains absorb the flavors.

Pour in the seasoned water and bring it to a boil. Make sure to scrape the bottom of the pot to deglaze and prevent sticking.

Once boiling, reduce the heat to low. Cover and simmer for 15 minutes. Remove the pot from the heat and let it steam for another 10 minutes.

Add the green parts of the green onions and a pat of butter. Gently fluff the rice and serve with the sauce, if using.