Preheat oven to 350°.
Combine first 4 ingredients in a bowl.
Arrange half of potato slices in a 13 x 9-inch baking dish coated with cooking spray, and sprinkle with 1/2 cup cheese mixture. Arrange half of parsnip over cheese mixture. Spread half of celeriac over parsnip. Repeat layers, ending with celeriac. Sprinkle with salt and pepper. Pour broth over top.
Cover and bake at 350° for 45 minutes. Uncover; sprinkle with 1/2 cup cheese mixture and breadcrumbs. Drizzle with butter. Bake an additional 20 minutes or until golden brown.