For the turnip and sweet potato gratin, preheat the oven to 350 degrees Fahrenheit. Peel and slice 3 medium turnips and 2 medium potatoes, slicing them into 1/4-inch-thick rounds. Arrange a single layer of both on an 8-by-8 inch baking dish. Season with salt and pepper, and sprinkle on 1/3 of a 1/4 cup of flour.
Repeat that process to make three more layers, continuing to season and use the rest of the flour. Dot the top with 2 tablespoons of cut-up butter. Next, slowly pour on 3/4 cup of chicken broth and 1/4 cup of dry white wine. Cover with foil and bake for 45 minutes. Increase the oven to 425 degrees Fahrenheit, remove the foil, and sprinkle on 1 cup of Gruyere cheese. Bake for 12 more minutes.
For the spinach gratin, preheat the oven to 425 degrees Fahrenheit. Melt 4 tablespoons of butter in a pan over medium heat. Add 4 cups of chopped onions, and saute for 15 minutes. Add 1/4 cup of flour and 1/4 teaspoon of nutmeg, stirring for 2 minutes. Add 1 cup of heavy cream and 2 cups of milk, cooking until thickened.
Add 3 pounds of defrosted, drained chopped spinach. Mix in 1/2 cup of grated Parmesan and season with salt and pepper. Transfer to a baking dish, and top with 1/2 cup each of Parmesan and Gruyere cheese. Bake for 20 minutes.Learn more about Vegetables