Preheat oven to 350 degrees F.
Butter and flour a 9 x 5 x 3 loaf pan and then line with parchment (parchment is optional but it helps insure that the cake releases from the pan).
In medium bowl combine the flour, salt and baking powder. Stir to combine.
In bowl of mixer cream the butter until light and fluffy.
Add in the sugar, mix to combine.
Add in the cream cheese, mix to combine and until light and fluffy.
Add in eggs one spoonful at a time.
Add in the vanilla and lemon zest. Mix to combine.
Scrape sides of bowl as needed.
With mixer on medium add in the flour mixture one spoonful at a time.
Mix until batter is smooth. Fold in the blueberries.
Pour batter into prepared pan.
Bake for 70-75 minutes. Or until toothpick inserted in center comes out clean.
Let cool completely.
Cream the butter and cream cheese together.
Slowly add in the powdered sugar one spoonful at a time.
Add in the vanilla.
Continue mixing until completely combined and smooth and creamy.
Spread onto cooled cake with offset spatula.
Sprinkle on blueberries and lemon zest.