Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.

In a large mixing bowl, cream together the softened butter and granulated sugar 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 ingredients to the wet mixture, alternating with the milk. Mix until just combined.

Gently fold in the blueberries, being careful not to break them.

Pour the batter into the prepared baking pan and spread it evenly.

Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted in the center comes out clean.

Let the cake cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.

Dust with powdered sugar before serving, if desired.