Preheat the oven to 350 °F (175 °C) and line a 9"x13" pan with a piece of parchment paper. If making muffins, line pans with 24 muffin liners.
Pour the milk into a large mixing bowl, add the apple cider vinegar, and give it a few stirs. Let it sit for 5 minutes. This is to create homemade dairy-free buttermilk. It's okay if it curdles and it's also okay if it doesn't curdle.
2 cups (480 ml) dairy-free milk of choice, 4 teaspoons apple cider vinegar
To the milk mixture, add the melted and still warm coconut oil, sugar, room temperature egg, and vanilla and stir until well combined.
2/3 cup (150 grams) neutral-tasting oil, 1 cup (200 grams) granulated sugar, 2 large eggs, 2 teaspoons vanilla extract
In a medium mixing bowl, stir together all the dry ingredients. Add the dry mixture to the wet and stir just until combined.
1 1/3 cup (176 grams) cornmeal, 2 2/3 cups (368 grams) flour, 1 1/2 teaspoons salt, 1 tablespoon + 2 teaspoons baking powder, 1 teaspoon baking soda
Pour into the prepared pan or muffin pans (fill them 2/3 full). Bake the bread for 23 minutes or muffins for 12-16 minutes. The edges should be very lightly browned and the top should feel firm. The toothpick test doesn't really work well with this bread. I recommend using a small fork to dig into the center just a bit to make sure it's fully done.
Let the bread cool completely in the pan. If making muffins, let sit for 5 minutes then turn out onto a wire rack to cool completely.
Cover the cooled bread / muffins. Can be kept at room temperature for 4 days or refrigerated for 6. They freeze great. I recommend reheating them a little before serving for the best, fluffy texture.