Bring the water or stock to a light boil and set aside.
Prepare a paper lid (cartouche) by cutting a circle of parchment paper to the diameter of your ovenproof sauté pan or pot with a lid.
Preheat the oven to 375˚F (190˚C).
Place a large sauté pan over low heat and melt the butter, then stir in the onion and cook gently for 2 minutes, or until fragrant.
Add the rice, mixing well so that the grains are well coated, and continue to cook for 2 minutes.
Pour the warm water or stock gently over the rice, add the bay leaf and thyme and season with salt and pepper.
Increase the heat to high to quickly bring the liquid to a simmer, then immediately switch the heat off.
Place the cartouche inside the pan so that it rests on the rice. Cover with a lid and slide the pan onto the middle rack of the oven.
Set a timer to cook for 17 minutes. When the time is up, taste the rice to check whether it's done; it should be tender and well puffed. If not, return it to the oven for a few more minutes.
When cooked, let the rice stand, covered, for 5 minutes.
Just before serving the rice, discard the cartouche, bay leaf and thyme, and to finish, stir through a dab of butter.
Use a fork to separate and loosen the grains a little before enjoying with your favorite main dish.