Warm a cast-iron skillet over medium heat; swirl in 1 tablespoon oil to coat.
Whisk cornmeal, flour, baking powder, baking soda, salt, and sugar in a medium bowl.
In another bowl, whisk buttermilk, beaten egg, and melted butter until smooth.
Pour wet mixture into dry and stir just until combined. Let batter rest 5 minutes.
Stir in a little warm water if the batter looks very thick and heavy.
Spoon 2 to 3 tablespoons batter per cake into the hot skillet, spreading slightly.
Cook until edges set and bottoms are deeply golden, 2 to 3 minutes.
Flip carefully and cook until the second side is golden and cooked through, 1 to 2 minutes.
Add more oil as needed and repeat with remaining batter, adjusting heat to maintain sizzle.
Serve hot with butter, honey, or maple syrup. Keep finished cakes warm in a 200°F oven.