Melt the butter in a large skillet. Add the onion, carrots, celery and mushrooms. Sautee until soft. Add in the garlic and fry for another 2-3 minutes.
Sprinkle in the seasoning and mix throughout. Pour in the chicken broth and stir until combined.
Add in the bread cubes and toss with a wooden spoon etc. to coat the cubes as much as you can with the mixture, trying not to squish the cubes.