Preheat oven to 350 degrees F. Grease a 9x13-inch baking dish with cooking spray or butter.

Cut French loaf into 1-inch cubes, removing the ends of the loaves with thick crusts. Spread bread on a baking sheet and toast for 15-20 minutes or until lightly browned. Remove from oven and let cool.

Meanwhile, prepare the vegetables. Heat a large saute pan over medium heat. Add bacon and cook until browned and crispy, stirring occasionally. Remove bacon with a slotted spoon and set aside.

In the same pan, add the leeks. Season with salt and pepper and saute until softened and lightly browned, about 8-10 minutes. Add mushrooms and continue to cook until mushrooms are softened, anothere 8-10 minutes.

Add garlic and thyme, stirring to combine. Add sherry and bring to a boil. Continue to cook until all of the liquid has evaporated. Season with salt and pepper and remove from heat. Add back bacon and parsley to vegetables, stirring to combine. Let cool slightly.

In a large bowl, whisk together half and half, chicken stock, eggs, and 1 cup shredded gruyere cheese. Add vegetable mixture and toasted bread, stirring until well combined. Let sit for 30 minutes.

Stir the filling once more and transfer to the prepared baking dish. Sprinkle remaining ½ cup gruyere on top and bake stuffing for 40-45 minutes or until golden brown. Remove from oven and serve.