1 ½cupsbuttermilk (or mix 1 ½ tbsp vinegar with 1 ½ cup milk)
Preheat oven to 375°F. Add butter to a 9-inch cast-iron skillet and place in the oven while preheating. Once the butter has completely melted and browned, remove from the oven, 10-15 minutes.
In a large bowl, whisk together the cornmeal, flour, baking soda, baking powder, salt, and sugar. In another bowl, whisk the buttermilk and eggs. Add the wet ingredients to the dry and whisk until combined. Pour immediately into the hot skillet.
Bake until the cornbread is golden brown and a skewer inserted in the middle comes out clean, 20-25 minutes. Remove from oven and cool 10 minutes before slicing.