Preheat the oven to 350 °F (175 °C) and line a muffin pan with 12 muffin liners or line an 8" x 8" pan with a piece of parchment paper.
Pour the milk in a large mixing bowl, add the apple cider vinegar, and give it a few stirs. Let sit for 5 minutes while preparing the dry ingredients.
1 cup (240 ml) milk, 2 teaspoons apple cider vinegar
In a medium mixing bowl, stir together all the dry ingredients. Set aside.
2/3 cup (88 grams) medium grind gluten-free cornmeal, 1 1/3 cup (123 grams) oat flour, 3/4 teaspoon salt, 2 1/2 teaspoons baking powder, 1/2 teaspoon baking soda
To the milk mixture, add the melted coconut oil, sugar and vanilla and stir until well combined.
1/3 cup (75 grams) coconut oil, 1/2 cup (100 grams) raw sugar, 1/2 teaspoon vanilla
Add the dry mixture and stir just until combined.
Pour into the prepared pan. Bake muffins for 12 minutes and bread for 20 minutes. A toothpick inserted in the middle should come out with a few moist crumbs but no wet batter.
Let the muffins cool for 5 minutes in the pan and then remove to a wire rack to cool completely. The bread can be eaten immediately but will be very difficult to cut – it's better to wait for 2-3 hours until it's firmed up just a little.
Store any leftovers in an airtight container for up to 3 days.