3 turnips, sliced into 1/8" rounds
2 parsnips, sliced into 1/8" rounds
6 C water
1 C heavy cream
1/3 C chicken broth
2 T flour
1 t salt
1/2 t freshly ground pepper
4 oz Gruyere, shredded
2 T butter
1/4 C panko
Preheat oven to 400 ° F. Combine the first three ingredients in a large pot and bring to a boil. Reduce heat and simmer until tender, about 7 minutes. Drain and let stand for 5 minutes. Coat two 8" casserole dishes with cooking spray, and split the vegetable mixture between them, layering vegetables evenly.
Combine milk, broth, flour, salt and pepper in a pot over medium-high heat and bring to a simmer. Cook 4 minutes, stirring constantly with a whisk until thick. Remove from heat, add cheese, stirring continuously until smooth. Pour sauce evenly over vegetables.
Melt butter in a skillet over medium-high heat. Add panko, toast until brown. Sprinkle panko over cheese mixture. Bake for 15 minutes or until bubbly. Let stand for a few minutes before serving.