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.
In a large mixing bowl, stir together the buttermilk, oil, sugar, room temperature egg (or chia egg), and vanilla and stir until well combined.
1 cup + 2 teaspoons (246 milliliters) buttermilk, 1/3 cup (80 ml) neutral-tasting oil, 1/2 cup (100 grams) granulated sugar, 1 large egg, 1 teaspoon 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.
2/3 cup (88 grams) medium grind gluten-free cornmeal, 1 1/3 cups (184 grams) Bob's Red Mill Gluten-Free 1-to-1 Baking Flour, 3/4 teaspoon salt, 2 1/2 teaspoons baking powder, 1/2 teaspoon baking soda
Pour into the prepared pan. Bake muffins for 12-16 minutes and bread for 20-25 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 in to the center just a bit to make sure it's fully done.
Let the muffins cool for 5 minutes in the pan and then remove to a wire rack to cool completely. Let the bread cool completely in the pan.
Store any leftovers in an airtight container for up to 3 days. It can be refrigerated for 5 days. It freezes great for up to 3 months.