Preheat oven to 350 degrees and position a rack in the center.

Lay the bacon slices in a cold 9- to 10-inch, heavy-bottomed ovenproof skillet (preferably cast iron). Cook over medium-low heat, turning frequently, until crispy. Remove the bacon; reserve.

Add the sliced onion to the pan and cook in the bacon grease until very soft, about 10 minutes.

Meanwhile, in a large bowl, whisk together the flour, cornmeal, salt, sugar and baking powder. In a medium bowl, whisk together the sour cream, milk and eggs. Pour into the flour mixture and fold together with a rubber spatula until just incorporated. Crumble the cooked bacon into small pieces and fold into the batter. Spread carefully over the onions in the skillet (its fine if the skillet is still hot).

Bake until a toothpick inserted in the center comes out clean, about 25 to 30 minutes. Let cool for 5 minutes, then loosen the sides of the bread with a spatula and invert onto a plate so that the onions face up. Bread is best enjoyed warm.

Meatless variation: Instead of using bacon, place a 9- to 10-inch, heavy-bottomed ovenproof skillet (preferably cast iron) over medium-low heat and add 4 tablespoons unsalted butter. When butter has melted, add the sliced onion and cook gently until very soft, about 10 minutes. Mix the batter and bake as directed.