Preheat oven to 400ºF. Lightly grease a 9-inch loaf pan.
In a large bowl, combine flours, baking powder, baking soda and salt. In another bowl, whisk together the maple syrup, egg, milk and melted butter. Pour the wet ingredients over the dry ingredients and stir just until combined. Gently fold in the blueberries and pour batter into prepared pan. Bake in a 400˚F oven for about 40-45 minutes or until golden brown and a toothpick comes out clean when inserted into the middle of the cake. Allow the cake to cool in pan for 5 minutes, then remove and let cool completely on a wire rack.
To make glaze, combine maple syrup, butter and pinch of salt in a microwave safe bowl. Microwave until butter has melted, 30-60 seconds. Stir in powdered sugar and microwave for about one more minute or until the sugar has completely dissolved. Pour warm glaze over cooled cake. If desired, poke loaf with a toothpick or skewer before pouring glaze for better absorption. Serve immediately.
This cake is best the day it is made, but can be made the night before if need be.