How to Make It
Preheat the oven to 350° and butter a 9-by-13-inch baking dish or very large enameled cast-iron skillet. In a saucepan of boiling water, cook the spinach just until wilted, about 30 seconds. Drain and cool under running water, then squeeze out as much water as possible. Finely chop the spinach.
In a large bowl, whisk the buttermilk with the egg yolks, cornmeal, flour, sugar, baking soda, salt, nutmeg, white pepper and the 3 tablespoons of melted butter. Fold in the chopped spinach.
In a clean bowl, using a handheld electric mixer, beat the egg whites until soft peaks form. Fold the whites into the batter and scrape it into the prepared baking dish.
Bake the spoon bread in the center of the oven for about 45 minutes, until golden. Let cool slightly, then serve.