Saute onions in 3 tablespoons butter; add cracker crumbs, bread crumbs, salt and sage.
Stuff trout; place in greased baking dish.
Cut shallow slits in trout.
Bake at 400 degrees for 10 minutes; baste with 2 tablespoons butter.
Add wine; bake for 10 minutes longer or until fish flakes easily with a fork.
Saute mushrooms in remaining butter.
Remove trout to heated platter.
Add drippings to mushrooms; blend well.
Spoon over trout.