COOK IT.
Set your grill to 350° F.
If brioche loaf is not already sliced, slice into 1-inch-thick slices. Divide loaf in half. You will grill/toast half of the bread, and leave the other half uncooked.
Toast half of the bread a few slices at a time by placing them directly on the grill grates & allowing them to toast for approx. 3 mins per side until grill marks appear. Once toasted, slice all of the brioche (both toasted and un-toasted) into 1-inch cubes. Set aside.
Heat a 12-inch cast iron skillet over indirect heat (away from the sear plate). Add the vegetable oil and half of the butter to the pan. As it starts to melt, add your onions & celery and sauté for 4-5 mins until onions begin to sweat.
Add sage, rosemary, thyme, Savory Smokehouse Rub, & salt to the pan & give it a stir.
Add second half of butter to the pan and then add your mushrooms & garlic. Cook these for at least 8-10 mins until the mushrooms have reduced down to approximately half of their original volume.
While the mushrooms are cooking, in a separate large mixing bowl add the egg & scramble it. Then pour in the vegetable broth and give it a stir. Add all of the cubed brioche to this egg-broth mixture and lightly toss until all bread is evenly covered. (Be gentle, as the brioche is delicate & can break down easily if mixed too aggressively at this stage.)
Once mushrooms have reduced to half their volume, pour the brioche mixture into the pan and give everything a gentle stir until it’s all evenly distributed.
Cover the pan with aluminum foil, ensure it is away from the sear plate / over indirect heat, close the grill & allow to bake for 30 mins.
Remove foil and allow to bake for a further 15 minutes or so, until top is toasty & inside is cooked through.
Remove from heat and allow to cool for 10 minutes before serving.