Combine all-purpose flour, baking powder, baking soda and salt in a small mixing bowl. Beat butter and granulated sugar together on medium-high speed.
Beat until fluffy-looking. About 2 minutes. Add egg and vanilla extract and beat again with the mixer until fully combined.
Add milk and dry ingredients. Start with 1/3 of the milk, then 1/3 of the dry, etc.) Beat on low until fully combined. After last addition, scrape sides of bowl with a rubber spatula. Give the mixture a few turns with the spatula to make sure it's fully mixed.