Grease and flour a 9×13-inch baking pan or line it with parchment paper.
2. Make the Cake Batter
In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
In a large bowl, beat the softened butter and sugar on medium speed until light and fluffy, about 3–4 minutes.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
Gradually add the dry ingredients to the butter mixture, alternating with the milk. Begin and end with the dry ingredients, mixing until just combined.
3. Bake the Cake
Pour the batter into the prepared baking pan, spreading it out evenly.
Bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean.