Preheat the oven to 375˚. Butter a 3-quart baking dish. Cook the bacon in a large pot or Dutch oven over medium-high heat, stirring occasionally, until crisp and browned, 7 to 8 minutes. Stir in the Brussels sprouts and a pinch of salt and cook, stirring, until wilted, about 2 minutes. Remove to a bowl.
Melt 6 tablespoons butter in the pot. Add the onion, celery, chestnuts, garlic, thyme, sage, 1 teaspoon salt and a few grinds of pepper. Cook, stirring occasionally, until the vegetables are softened, about 6 minutes. Add the chicken broth and bring to a simmer, then remove from the heat. Let cool slightly, about 5 minutes.
Whisk the eggs in a large bowl. Add the bread cubes, Brussels sprouts mixture, vegetable-broth mixture and parsley; stir until well combined. Transfer to the prepared baking dish, dot with the remaining 2 tablespoons butter and cover with foil.
Bake the stuffing until hot, about 30 minutes. Uncover and bake until golden brown, 25 to 30 minutes. Let cool at least 15 minutes before serving.