Preheat the oven to 350 F
Cream butter with powdered sugar until light and fluffy. Cream thoroughly, this is an important to make your cake fluffy. Add in the orange and lemon zest and mix until incorporated.
Add the egg and vanilla extract and beat until combined.
Add coconut flakes and mix until combined.
Toss the blueberries with flour, then whisk together the remaining flour, baking powder and salt.
Add the flour mixture to the batter a little at a time, alternating with buttermilk. This is also important to get that heavenly fluffiness.
Gently fold in the blueberries.
Grease a 9" square casserole with butter.
Spread batter into pan and sprinkle with sugar.
Bake for 35 to 45 minutes. Check the center with a toothpick. You may need to bake for extra 10 minutes is necessary.
Let cool at least 15 minutes before serving. It may crumble (in which case serve using a teaspoon as I did) so you might wanna cool completely before cutting and serving.