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