Buttermilk-Cinnamon Bread

1. Preheat oven to 375ºF; grease a 9- by 5- by 3-inch loaf pan with butter.
2. Whisk together the flours, brown sugar, cinnamon, baking powder, baking soda, and salt in a large bowl. Stir in the buttermilk and sparkling water with a wooden spoon, being careful not to over-mix.
3. Pour the batter into the loaf pan, drape a piece of plastic wrap on top, and let it sit in a warm place for 5 minutes.
4. Pour the melted butter on top; bake until a toothpick inserted inside comes out clean, about 40 to 45 minutes. Cool completely before slicing.