Preheat the oven to 425 degrees Fahrenheit. Butter an 8-by-12-inch baking dish. In a glass measuring cup, combine the cream with 1/4 cup of the Parmesan and the salt, pepper and nutmeg.
In a medium skillet, melt the butter. Add the spinach and minced garlic and cook over moderately high heat, tossing, until the spinach is wilted, about 1 minute.
Spread the potato slices in the baking dish and cover with the spinach. Pour the cream over the top and shake the dish to distribute evenly. Sprinkle the remaining 2 tablespoons of Parmesan over the top and bake for about 20 minutes, or until browned, bubbling and the potatoes are tender. Let rest for 5 minutes before serving.