How to Make It
Heat oven to 375° F. Butter a 9-by-13-inch baking dish. Divide the bread between 2 rimmed baking sheets and bake until dry and crisp, 10 to 12 minutes.
Meanwhile, melt the butter in a large skillet over medium heat. Add the onions, 1 teaspoon salt, and ¼ teaspoon pepper. Cook over medium-low heat, stirring occasionally, until deep golden brown, about 1 hour. Add the wine and cook until evaporated, 2 to 4 minutes; transfer to a large bowl and let cool for 10 minutes.
Add the bread, broth, eggs, chives, thyme, and ½ teaspoon salt to the onions and toss to combine. Transfer to the prepared baking dish. Cover with buttered foil and bake for 20 minutes. Uncover and bake until browned, 20 to 30 minutes more.