How to Make It
Preheat oven to 400°F.
Arrange bread cubes in a single layer on a rimmed baking sheet. Bake at 400°F for 20 minutes or until golden, stirring after 10 minutes. Place the bread cubes in a large bowl.
Reduce the oven temperature to 350°F.
Heat a large skillet over medium-high. Add 1 tablespoon butter and 1 tablespoon oil; swirl until butter melts. Add mushrooms; cook 10 minutes or until browned and liquid evaporates. Add vinegar, scraping pan to loosen browned bits. Add mushroom mixture to bread cubes; toss to combine.
Return skillet to medium-high. Add remaining 1 tablespoon oil; swirl. Add onion, celery, thyme, and garlic; sauté 10 minutes. Remove pan from heat; stir in parsley, pepper, and salt. Add onion mixture to bread mixture; toss to combine.
Melt remaining 2 tablespoons butter in skillet. Combine butter, stock, and eggs in a bowl, stirring with a whisk. Drizzle stock mixture over bread mixture; toss. Let stand 10 minutes or until liquid is absorbed, stirring occasionally. Spoon bread mixture into a 2-quart glass or ceramic baking dish coated with cooking spray. Bake at 350°F for 25 minutes or until browned.