2 cups peeled and thinly sliced parsnips (about 12 ounces)
2 tablespoons butter
2 teaspoons all-purpose flour
1 cup evaporated milk
1 teaspoon snipped fresh thyme leaves
1 clove garlic, minced
5 tablespoons finely shredded Parmesan cheese
Fresh thyme (optional)
salt and pepper to taste
Preheat oven to 375 degrees F. Coat a 1 1/2-quart oval baking dish or casserole with cooking spray. Arrange sliced celery root and parsnips in the prepared baking dish.
Place a small saucepan over medium heat. Melt the butter, then whisk in the flour. Cook the flour and butter mixture for 1 minute, then slowly whisk in the thyme. Add the fresh thyme and garlic and cook, stirring constantly, until the sauce thickens. Season generously with salt and pepper.
Pour the thickened sauce over the arranged vegetables and sprinkle with the Parmesan cheese. Bake, covered, 40 minutes. Bake, uncovered, about 15 minutes more or until vegetables are tender and top is lightly browned. Let stand 10 minutes before serving. If desired, garnish with additional fresh thyme.