Preheat the oven to 375 degrees F. Butter a shallow 3-quart baking dish. Cook the bacon in a large nonstick skillet over medium-high heat, stirring, until crisp, about 5 minutes. Add 6 tablespoons butter, the onions, scallion whites and a pinch of salt. Cook, stirring, until softened, about 5 minutes. Stir in the rosemary. Add the chicken broth and 1 teaspoon salt; bring to a simmer, then remove from the heat.
Whisk the eggs in a large bowl. Whisk in the Parmesan, parsley and 1 tablespoon pepper. Stir in all but 2 tablespoons scallion greens. Stir in the bread cubes and bacon mixture.
Transfer the stuffing to the prepared dish. Dot with the remaining 2 tablespoons butter. Cover with foil and bake 30 minutes. Uncover and bake until browned, 20 to 30 more minutes. Top with the reserved scallion greens.
Make the stuffing 2 to 3 days ahead; cover and refrigerate. Reheat at 325 degrees F, covered, until hot, then drizzle with broth or melted butter if it looks dry. Bake, uncovered, a few more minutes until crisp.