Preheat oven to 350 degrees F (175 degrees C). Bring chicken broth to a boil in a medium saucepan.
In a 1 1/2 quart baking dish, mix chicken broth, uncooked wild rice, water chestnuts, 2 tablespoons butter and salt.
Cover, and bake in the preheated oven 30 minutes.
While rice mixture is baking, melt remaining butter in a medium skillet over medium heat. Place mushrooms and onion in skillet, and slowly cook and stir until tender. Stir mushrooms and onion into the wild rice mixture, cover, and continue baking 30 minutes, or until liquid has been absorbed.