Creamiest Mushroom Chicken Casserole

Ingredients

• 1/2 cup plus 2 tablespoons unsalted butter, divided
• 1 (16-ounce) package fresh button mushrooms, sliced
• 2 (4-ounce) packages fresh gourmet-blend mushrooms
• 1/2 cup yellow onion, diced
• 3 cloves garlic, minced
• 1/2 cup all-purpose flour
• 1 cup chicken broth, room temperature
• 1 cup heavy whipping cream, room temperature
• 4 ounces cream cheese, softened
• 4 cups chicken breasts, boneless and skinless, cooked and shredded
• 1 tablespoon plus 1/4 teaspoon kosher salt, divided
• 1/2 teaspoon ground black pepper
• 1/4 teaspoon celery salt
• 2 cups sourdough bread, torn into pieces
• fresh parsley, to taste, chopped, for garnish