Preheat oven to 300°F (150°C). Spread 10 cups 1-inch bread cubes (French, Italian, or sourdough) in a single layer on a large baking sheet. Bake 7–10 minutes, until dried and lightly toasted. Remove from oven and increase oven temperature to 350°F (175°C).
While the bread toasts, heat a large skillet over medium heat. Add 1 lb sweet or spicy sausage (casings removed) and cook, breaking up with a wooden spoon or spatula, until browned and cooked through, about 10 minutes.
Transfer the cooked sausage to a plate lined with paper towels to drain excess grease. Pour off most of the fat from the skillet, leaving any browned bits.
In the same skillet, melt 1/2 cup unsalted butter over medium heat. Add 2 cups diced yellow onion and 1 cup chopped celery. Cook, stirring occasionally, until the vegetables are tender, about 5–7 minutes.
Add 3 cloves minced garlic, 2 tablespoons chopped flat-leaf parsley, 1 tablespoon chopped fresh sage, 1 teaspoon kosher salt, and 1/2 teaspoon freshly ground black pepper to the skillet. Cook, stirring, until the garlic is cooked but not browned, about 3–5 minutes.
In a large bowl, combine the toasted bread cubes, drained sausage, and the cooked vegetable mixture. Pour 2 cups chicken broth over the mixture and stir gently until the bread is evenly moistened and the liquid is mostly absorbed. Stir in 3/4 cup dried cranberries, if using.
Transfer the stuffing to a greased 9×13-inch baking dish and spread evenly. Bake at 350°F (175°C) for 30–35 minutes, until the top is browned and the stuffing is heated through.
Remove from oven and serve warm.