First, preheat your oven to 350F. Then, grease your loaf pan and optionally, line it with parchment paper.
In a liquid measuring cup or medium-sized bowl, mix together the whole milk and vinegar. Let it sit for at least 5 minutes. It will curdle slightly and mimic buttermilk.
1 cup whole milk, 1 tbsp white vinegar
Meanwhile, add all dry ingredients to a large bowl and whisk until combined.
1.5 cups gluten free 1-to-1 flour, 1.5 cups gluten free medium-grind cornmeal, ½ cup cane sugar, 1 tsp baking powder, ½ tsp baking soda, ½ tsp kosher salt
In another large bowl, add all of the wet ingredients, including the homemade "buttermilk." Whisk until smooth.
½ cup salted butter, 2 large eggs
Pour wet ingredients into the dry ingredients and stir with a spatula. You don't want to mix it completely - stop when there's still plenty of flour visible.
Add in the zucchini, cheddar and chives and stir with the spatula until fully incorporated and no flour remains visible. Do not over-stir! The batter will be pretty thick.
1.5 cups finely grated zucchini, 1 cup shredded sharp cheddar cheese, ¼ cup chopped chives
Pour batter into prepared loaf pan and spread out evenly. Transfer to the pre-heated oven and bake for 1 hour.
Remove loaf from the oven and allow it to cool slightly before cutting into slices. Enjoy as is or with a bit of butter!