In a 10-inch cast-iron skillet, heat 1 tablespoon oil over medium-high heat. Add sausage; reduce heat to medium, and cook until browned, about 5 minutes. Remove sausage using a slotted spoon, and let drain on paper towels. Place skillet with drippings in oven until very hot, about 6 minutes.
In a large bowl, whisk together cornmeal, flour, baking powder, baking soda, and salt. In a small bowl, whisk together buttermilk, egg, and remaining 2 tablespoons oil. Make a well in center of cornmeal mixture; add buttermilk mixture, stirring just until combined. Reserve ⅓ cup sausage. Stir remaining sausage into batter. Carefully remove hot skillet from oven; add batter, smoothing top. Sprinkle with reserved ⅓ cup sausage.
Bake until a wooden pick inserted in center comes out clean, about 15 minutes. Let cool in skillet for 10 minutes. Serve warm.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/smoked-sausage-cornbread/