Preheat oven to 375ºF. Coat loaf pan with nonstick cooking spray.
Whisk together all-purpose flour, whole wheat flour and baking powder in large bowl until combined.
Add maple syrup, 3 tablespoons melted butter and hard cider. Stir until just combined and no dry flour remains.
Spread batter evenly into prepared loaf pan. Sprinkle oats over batter and drizzle with remaining melted butter.
Bake 45 minutes, or until top is golden brown and toothpick inserted into center comes out clean.
Cool 10 minutes in pan, then remove from pan and transfer to wire rack to cool completely.
While bread cools, whisk together butter, syrup and kosher salt in medium mixing bowl until smooth.
Transfer to serving bowl and serve at room temperature.
Spread butter on slices of bread and sprinkle with flake salt.
