In a large mixing bowl using a stand mixer or electric hand mixer, cream together the softened butter, cream cheese, and granulated sugar until light, fluffy, and well combined.

Add the eggs one at a time, beating well after each addition, then mix in the vanilla extract and lemon zest.

In a separate bowl, whisk together 2 cups of flour, baking powder, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. The batter will be thick; be careful not to overmix.

In a small bowl, toss the blueberries with the reserved 1 tablespoon of flour. This helps prevent them from sinking to the bottom of the loaf.

Gently fold the flour-coated blueberries into the batter using a spatula.

Pour the batter into the prepared loaf pan and smooth the top evenly.

Bake for 50 to 65 minutes. Check for doneness by inserting a toothpick into the center; it should come out clean or with a few moist crumbs. If the top browns too quickly, tent loosely with foil.

Allow the loaf to cool in the pan for about 15 minutes, then transfer to a wire rack to cool completely before slicing.