Preheat the oven to 350°F. Melt the butter over medium heat in an ovenproof saucepan with a lid. Chop two of the shiso leaves and cook them in the butter for 30 seconds.
Add the rice and cook, stirring, until the rice becomes transparent, just a couple of minutes. Add 1 1/2 cups water and some salt and pepper. Bring to a boil, cover, place in the oven, and set a timer for 10 minutes.
While the rice is cooking, mince the remaining shiso. When the 10 minutes are up, remove the rice but do not uncover; let it rest in a warm place for another 10 minutes. Stir in the remaining shiso, adjust the seasoning, and serve immediately.
