Step 1Trim the crust from the loaves and cut the bread into 1/3-inch cubes. Set aside.
Step 2In a large skillet heated over medium heat, add the olive oil. Stir in the garlic and cook, stirring until fragrant, 1 to 2 minutes. Add the bread cubes (this may be done in batches if necessary), stirring to evenly coat with the oil. Season with the Old Bay, pepper and garlic salt. Remove from heat and spread on a parchment-lined rimmed baking sheet, removing and discarding the garlic cloves.
Step 3Set aside in a cool dry place overnight to dry out.
Step 1Combine the salt, black pepper, garlic salt and cayenne pepper in a spice or coffee grinder and pulse until the spice blend has the consistency of sand. Store the spice blend in a sealed container in a cool, dry place up to 1 month.
Step 1In a very large skillet heated over medium-low heat, melt a tablespoon or so of butter and sweat the celery and shallots with the kosher salt until softened and lightly golden, 8 to 10 minutes. Push the shallots and celery to the side of the pan and add the garlic (add another tablespoon or so of butter so the pan is not dry), cooking until the garlic is golden, 2 to 4 minutes, then push the garlic over with the shallot and celery. Flip the shallot and celery mixture so it continues to heat evenly.
Step 2Add another tablespoon of butter, then the mushrooms, cooking until they are golden brown, 10 to 12 minutes. Stir in the apples and cook until they are golden, then add the herbs.
Step 3Deglaze the pan with the wine, reducing the wine until it is completely dry. Stir in the chicken broth and gravy, and season with about 1 teaspoon spice blend, or to taste. Remove from heat and discard the garlic cloves, rosemary and sage.
Step 4In a large bowl, combine the croutons with the mushroom mixture, tossing to combine. Add additional stock if you’d like for a more moist dressing.
Step 5Set the mixture aside until it comes to room temperature. Meanwhile, generously butter a casserole dish, and season with a light sprinkling of salt and several grinds of black pepper. Refrigerate the dish until the butter is chilled. Meanwhile, heat the oven to 425 degrees.
Step 6Once the dressing is cooled to room temperature, stir in the chicken fat and 1 cup softened butter, along with the chopped parsley.
Step 7Drop spoonfuls of dressing into the casserole dish. Do not flatten the dressing but keep the rustic texture, making sure that there are “peaks and valleys” to give the dressing added texture and crunch as it bakes. For added crunch, dot each “peak” with melted butter.
Step 8Place the dressing in the oven and bake until crispy golden, about 30 minutes. Remove from the oven and crumble over the fried sage leaves.