2. Melt 2 tablespoons butter in a 1-quart Dutch oven. Add onion and saute until soft. Add green pepper and mushrooms and saute for 5 minutes. Remove mixture and set aside.
3. In same pot melt remaining 2 tablespoons butter. Add rice and saute until opaque. Add stock and salt, and stir. Add reserved vegetables and season with pepper and thyme.
4. Cover and bake for 30 to 40 minutes, or until all the liquid has been absorbed and rice is done.