Preheat oven to 350 degrees.

Melt butter in a large skillet over medium-high heat, and sauté the thinly sliced shallots until softened.

Add the mushrooms to the pan and cook until they have lightly browned; add minced garlic to the pan and cook for another minute or two.

In a baking dish, arrange the cubed brioche and pour the shallot-mushroom mixture over the bread and half of the fresh thyme, tossing to combine.

Then stream in the warm chicken broth and toss until the bread absorbs all of the liquid.

Season to taste with salt and pepper, and then bake at 350 degrees for 20 minutes. Remove from oven and garnish with the remaining fresh thyme.