Cook the onions and butter slowly in a flameproof casserole over medium heat until soft but not browned. Blend the rice into the butter and onions and stir over moderate heat for several minutes, not letting the rice brown. The grains will get translucent first, then turn a milky white color.
As soon as the rice looks milky, add the boiling stock. Add the herbs and salt and pepper to taste. Bring to a simmer, then cover and place in the oven.
As soon as the liquid maintains itself at a slow boil (4-5 minutes), reduce the heat to 350 and continue to bake until the liquid has been absorbed (about 15 minutes).
Remove from oven, uncover and fluff with a fork before serving (for al dente rice. FOr more tender rice, let stand, covered, for 10 minutes).