Place a 10-inch cast iron skillet in the oven and preheat to 425°F (220°C). Allow the skillet to preheat properly—it's the secret behind that signature crispy crust.
In a large bowl, whisk together the cornmeal, flour, sugar, baking powder, baking soda, and salt.
In a separate bowl, beat the eggs lightly, then add buttermilk and whole milk.
Pour the wet ingredients into the dry ingredients and stir just until combined. Don't overmix—a few small lumps are perfect.
Gently fold in the melted butter.
Carefully remove the hot skillet from the oven using thick oven mitts. Add the vegetable oil and swirl to coat the bottom and sides completely.
Pour the batter into the hot skillet. Return the skillet to the oven immediately and bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean and the top is golden brown.
While the cornbread bakes, make your honey butter by mixing softened butter with honey and salt until completely smooth and creamy. Add cinnamon or vanilla if using.
Allow the cornbread to cool in the skillet for 10 minutes before serving. This resting period allows the internal structure to set properly.
Slice and serve warm with honey butter.