1/4 cup unsalted butter melted and slightly cooled
1 large egg
With the oven rack in the bottom position, heat the oven to 350 degrees. Grease a 9 x 5-inch loaf pan with nonstick cooking spray. Mix the flours, oats, baking powder, salt, and baking soda together in a large bowl. Whisk the buttermilk, honey, melted butter, and egg together in a large measuring cup, then add it to the dry ingredients. Stir until just combined.
Pour the batter into the prepared pan, and bake until the loaf is golden brown and a toothpick inserted into the center comes out clean, 55 to 60 minutes. Cool in the pan on a rack for 10 minutes, then turn out onto the rack. Cool the bread to room temperature, then cut into 12 slices.