6 ounces bacon, diced
1 small white onion, diced
3 ounces fresh baby spinach, roughly chopped
4 large eggs, beaten
2 cups whole milk
2 cups coarse cornmeal, such as Bob's Red Mill Coarse Grind Cornmeal
2/3 cup shredded Parmesan cheese, divided
1 teaspoon salt
Freshly ground black pepper
4 cups boiling water
Preheat the oven to 350°F and lightly grease a 9-x-13-inch baking dish.
Cook the bacon in a deep skillet over medium heat until crispy around the edges, 8 to 10 minutes. Add the onion and cook for an additional 3 to 4 minutes, or until the onion has softened. Stir in the spinach and cook for about 30 seconds, just long enough to barely wilt the spinach. Remove the skillet from the heat.
Beat the eggs in a large bowl and whisk in the milk, then whisk in the cornmeal and 1/3 cup of Parmesan cheese. Fold in the cooked bacon and spinach mixture, along with the salt and a generous quantity of black pepper. Pour into the prepared baking dish.
→ Make-Ahead Note: At this point the casserole could be covered and refrigerated overnight, then baked in the morning.
When ready to bake, pour in the 4 cups of boiling water and whisk to combine in the dish. Bake uncovered for 50 to 60 minutes. After 20 minutes, whisk thoroughly, moving the polenta from the edges of the pan in to the center, and moving the center of the polenta out, to ensure the polenta is baking evenly. Continue baking until the polenta looks firm and golden-brown on top, and a knife comes out clean. Sprinkle the remaining 1/3 cup Parmesan over top while the casserole is still hot.
Serve warm, cold, or hot. The polenta will be fairly soft while hot, but will firm up as it cools. Leftovers will keep in a covered container in the refrigerator for up to 5 days.
Updated from recipe originally published March 2014.