How to Make It
Preheat oven to 350˚F. Melt 2 tablespoons of the butter in a large skillet set over medium. Add cabbage, celery, onions, and garlic, and cook, stirring often, until tender, 10 to 15 minutes. Transfer to a 3-quart lightly greased (with cooking spray) baking dish.
Melt 2 tablespoons of the butter in a medium saucepan over medium; whisk in flour, and cook, whisking constantly, until smooth and thick, about 1 minute. Gradually add milk to saucepan, whisking constantly to remove any clumps. Cook, whisking constantly, until thickened and smooth, about 3 minutes. Remove from heat, and whisk in Worcestershire, salt, pepper, and 1/2 cup of the Parmesan until smooth. Pour sauce over cabbage mixture.
Place remaining 1 tablespoon butter in microwavable bowl, and microwave on HIGH until melted, about 30 seconds. Add breadcrumbs and remaining 1/2 cup Parmesan to melted butter, and stir until combined. Sprinkle breadcrumb mixture evenly over cabbage.
Bake in preheated oven until casserole is bubbly and breadcrumbs are golden, 20 to 25 minutes.