Preheat oven to 375F.

Set a large frying pan over medium-low heat, add butter, celery, onion and mushrooms, season with salt. Cook for 6-8 minutes or until softened.

Combine bread with celery mixture and sage in a large bowl. Add 1 cup of broth and stir to combine.

Dump into a 8x8" baking dish, Bake in the centre of the oven for 30, check during last 10 minutes and cover with foil if beginning to brown too much.