Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking pan or line it with parchment paper.

In a large mixing bowl, combine the softened butter and cream cheese. Beat until creamy and well-blended. Add the sugar and mix until light and fluffy.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry mixture to the wet mixture, stirring until just combined.

Gently fold the fresh blueberries into the batter, being careful not to crush them.

Pour the batter into the prepared baking pan and smooth the top with a spatula. Optionally, sprinkle a little extra sugar over the top.

Bake for about 30 to 35 minutes or until a toothpick inserted comes out clean.

Let the cake cool in the pan for a few minutes before transferring it to a wire rack. Serve warm or at room temperature.