Preheat the oven to 425 degrees . In a medium bowl, whisk together the flour, cornmeal, sugar, baking powder, salt, baking soda and pepper. In a small bowl, whisk together the buttermilk and eggs.
In a large (10-inch) cast-iron skillet, cook the bacon over medium heat until golden but not crisp, about 5 minutes. Stir in the scallion whites and butter. Cook, stirring occasionally, until the scallions soften, about 3 minutes.
Whisk the buttermilk mixture into the flour mixture to combine. Whisk in the scallion greens, then mix in the hot bacon mixture, leaving some fat in the skillet.
Immediately pour the batter back into the hot skillet. Transfer to the oven and bake until a toothpick inserted in the center comes out clean, about 20 minutes. Let cool in the skillet for 5 minutes before serving.