1. Pour 1 1/2 inches of water into a large saucepan, add 1/2 teaspoon of the salt and bring to a boil over high heat.

2. Cut 1 inch from the tops of the onions to make a flat surface.

3. Add the onions to the water, return to a boil and reduce the heat to moderate.

4. Cook, covered for 10 to 15 minutes or until the onions are almost tender but retain their shape.

5. Meanwhile melt the butter in a heavy 10 inch skillet over moderately low heat.

6. Add the mushrooms and saute for 3 to 5 minutes or until tender. Set aside.

7. Drain the onions on a platter lined with paper toweling.

8. When cool enough to handle gently scoop out the insides with a serving spoon, leaving the shells 3/8 to 1/2 inch thick. Make sure that the bottom of each shell remains intact.

9. Chop up the pulp.

10. Preheat the oven to 350.

11. In a medium bowl mix 1 cup of the chopped pulp, the mushrooms, rice, pecans, egg and salt, thyme, pepper and nutmeg until well blended.

12. Stuff the onions with equal amounts of mixture and place in a lightly greased 13 by 9 by 2 baking dish.

13. Bake covered for 45 minutes, uncover, bake 10 minutes longer.