1. Preheat the oven to 350 degrees. Butter and flour a 8.5-inch loaf pan. Set aside.
2. In the bowl of a stand mixer, combine the butter and sugar. Beat with the paddle attachment until light and fluffy -- about 2 minutes. Add the eggs and beat until well combined. Add the vanilla and beat until combined.
3. In a medium bowl, whisk together the whole wheat flour, all purpose flour, baking powder and salt. With the stand mixer running on its lowest speed, add a little at a time until incorporated. Add the blueberries and beat briefly to combine.
4. Pour the bread batter into the prepared loaf pan and spread into an even layer.
5. Bake for about 1 hour, until
golden and cooked through.
6. Cool completely before slicing.