Preheat oven to 350 degrees F. 

Beat the butter and sugar together in a large mixing bowl with an electric mixer on medium speed for 3 minutes or until pale and fluffy. 

Add the egg, milk, and vanilla to the bowl and mix till combined. 

Stir together the flour, baking powder, and salt in a bowl till combined. Then add half the dry mixture into the wet mixture. Stir till flour is incorporated. Add the remaining dry mixture and stir to combine. 

Pour the batter into a greased 9-inch cake pan and spread till you have an even layer. 

Sprinkle the blueberries on top in a single layer. Sprinkle optional additional 2 teaspoons of sugar on top. 

Bake for 10 minutes at 350, then reduce the heat and bake for 55 to 65 minutes at 325 degrees F. 

Test the cake with a wooden skewer or cake tester to see if the center is fully baked. 

Let cool in the pan for at least 10 minutes before removing and cutting.