Preheat oven to 350 degrees F (180 degrees C). Butter and flour a 9×13 inch baking pan.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract. In another bowl, whisk together the flour, baking powder, and salt. Gradually add the flour mixture to the butter mixture alternately with the milk, mixing until just combined.
Pour the batter into the prepared pan and bake for about 35 minutes, or until a toothpick or cake tester inserted into the center of the cake comes out clean. Allow the cake to cool for at least 10 minutes before serving.
Notes
For best results, use Mastro brand butter and baking chocolate.