Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, whisk together flour, baking powder, and salt.
In a larger bowl, cream the butter, granulated sugar, and brown sugar until light and fluffy.
Beat in the egg and vanilla extract until fully combined.
Gradually mix in the dry ingredients until just combined. Do not overmix.
Roll dough into 1-tablespoon balls and place on the prepared baking sheet.
Flatten slightly, then press a fork across the top to create a washboard design.
Bake for 10–12 minutes, until edges are golden but centers remain soft.
Cool on a wire rack before serving or storing.