Whisk the flour, baking powder, baking soda, and salt together in a medium bowl or large mixing bowl. Set aside.
1 ⅔ cups all-purpose flour, ½ teaspoon baking powder, ¼ teaspoon baking soda, ½ teaspoon salt
Using a hand mixer, electric mixer, or stand mixer fitted with a paddle attachment, beat the softened butter and sugar together in a large bowl until creamed, about 2 minutes.
½ cup unsalted butter, 1 cup granulated sugar
Add the egg and vanilla extract and beat on high speed until combined. Scrape down the bottom and sides of the bowl as needed.
1 large egg, 2 teaspoon vanilla extract
With the mixer running on low speed, add the dry ingredients ⅓ at a time, alternating with the milk, starting and ending with the flour. Scrape the bottom and sides of the bowl to ensure all the flour is incorporated. Do not overmix.
1 cup whole milk
Pour the batter into the prepared pan. Bake cake for 30-35 minutes or until a toothpick inserted in the center comes out clean. If the top begins browning too quickly in the oven, loosely place a piece of aluminum foil on top.
Allow the cake to cool completely in the pan set on a wire rack. Meanwhile, prepare the frosting.