Preheat oven to 375˚F.
Heat an 10.25" seasoned cast iron skillet over medium-low heat on the stove while you prepare batter.
Whisk milks and apple cider vinegar together and let stand for a few minutes to thicken.
Whisk cornmeal, flour, sugar, salt, baking powder, baking soda together in a mixing bowl.
Whisk oil into thickened milk mixture, then pour into into the dry mixture.
Stir together until combined, about 1 minute.
Flick water droplets from fingertips onto the the cast iron skillet to test if it is hot. Water drops should sizzle and evaporate.
When skillet is hot, add canola or grape-seed oil or vegan butter and swirl skillet, holding handle with an oven mitt, so oil/melted butter coats bottom and part of sides.
Pour batter into the hot skillet and scrape down sides of bowl. Batter should sizzle when it hits the hot skillet.
Smooth top with a spatula and transfer skillet to preheated oven.
Bake at 375˚F for about 25 minutes until cornbread is golden with a cracked top.
Remove from oven and let cornbread cool for 10 minutes before cutting into it. Serve cornbread warm or at room temperature.