Step 1

Preheat oven to 300 degrees. Divide bread between 2 rimmed baking sheets and spread in a single layer. Bake, stirring a few times, until crisp and dry, about 40 minutes. Let cool. Break a piece open to make sure it's dried all the way through; if not, bake a few more minutes. Transfer to a large bowl.

Step 2

Melt butter in a large skillet over medium-high. Add onions, celery, and 2 teaspoons salt. Cook, stirring occasionally, until vegetables are soft and golden in places, 7 to 9 minutes. Add garlic, sage, and 1/4 teaspoon pepper; cook 1 minute. Pour in wine; cook until mostly evaporated, 1 to 2 minutes. Remove from heat.

Step 3

Increase oven temperature to 375 degrees. Brush a 2 1/2-quart baking dish with butter. Transfer onion mixture to bowl with toasted bread; add parsley. Drizzle with stock, stirring to combine. Stir in eggs to evenly coat. Transfer to prepared baking dish. Top with buttered parchment; loosely wrap with foil. (If making ahead, refrigerate at this point until you're ready to bake.) Bake 20 minutes. Uncover; continue cooking until golden on top, about 20 minutes more. Serve, with more parsley sprinkled on top.