Preheat your oven to 350°F (175°C).
Grease and flour a 9x13-inch baking pan.
In a large bowl, cream the softened butter and sugar together until light and fluffy.
Add the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract.
In another bowl, whisk together the flour, baking powder, and salt.
Gradually add the dry ingredients to the butter mixture, alternating with milk.
Mix until just combined; do not overmix.
Pour the batter into the prepared baking pan and smooth the top.
Bake for 50-60 minutes or until a toothpick inserted in the center comes out clean.