Preheat oven to 400°.
Place the vegetable oil in a 10-inch cast iron pan set over a medium heat.
Once the oil is hot, add the sausage to the pan and render it, stirring often until the most of the fat has been released and the meat is crispy, about 7 to 8 minutes.
Remove the sausage from the pan, reserving the meat and place the pan with the sausage fat in the oven.
Combine dry ingredients with the cheddar cheese and green onions, and stir in the buttermilk, the remaining 1/4 of vegetable oil and eggs, mixing just until dry ingredients are moistened.
Fold the rendered sausage into the corn bread batter.
Remove the pan from the oven, and pour the corn bread batter into the cast-iron pan.
Bake for 25 to 30 minutes or until light golden brown and a wooden toothpick inserted in the center comes out clean.
Serve warm as a side for gumbo.