Preheat the oven to 400?F.
Heat 2 tablespoons oil in a large 9- or 10-inch cast-iron skillet over medium heat. Once the oil is hot, add the sausage and cook, stirring often, until most of the fat has been released and the meat is crisp, 7 to 8 minutes. Remove the sausage from the skillet and set aside on a plate. Place the skillet with the sausage fat in the oven. In a large bowl, combine the flour, cornmeal, baking powder, and salt and whisk to combine. Stir in the Cheddar cheese and green onions. Combine the buttermilk, the remaining 1/4 cup oil, and the eggs in a medium bowl and whisk to combine. Add this buttermilk mixture to the dry ingredients and stir, mixing just until the dry ingredients are moistened. Fold the sausage into the cornbread batter. Remove the skillet from the oven and add the cornbread batter. Bake for 25 to 30 minutes, or until light golden brown and a wooden toothpick inserted in the center comes out clean. Allow the cornbread to sit for 5 minutes and then cut into wedges.
Makes 10 to 12 servings