Grease a round cake pan (8- or 9-inch diameter will work, just make sure it comes up at least 2 inches) with cooking spray or butter.
Add about 1 tablespoon of flour to the pan, move it all around, and tap off all the excess.
In a large bowl, add butter and ½ cup sugar and beat with mixer until soft and creamy.
Add eggs, milk, and vanilla. Beat well.
Add flour, baking powder, and sea salt; and give this powder mixture a little mix with a spoon and then beat with mixer on low until just combined. Don’t overbeat in this step.
Pour into cake pan and bake until a fork poked inside comes out clean (about 25 min).
Let cool for 10 minutes, then remove cake from pan and let cool for another 10 minutes before splitting cake in half lengthwise (serrated knife works best for this).