Examine the rice for foreign objects, but do not wash.
Heat the olive oil in the bottom of a heavy casserole until it begins to bubble. Add the onion and saute until translucent. Add the rice and stir to coat well with oil before adding the bay leaf, salt, pepper and the hot broth. Quickly bring to a boil, place a tight fitting lid on the pot and place into the oven.
Cook the rice for 18 to 20 minutes before removing from the oven. Stir in the butter and the chopped mint and serve.