Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a medium bowl, whisk together the flour, baking powder, and sea salt. Set aside.

In a large mixing bowl, beat the softened butter, granulated sugar, and brown sugar together until light and fluffy, about 2-3 minutes.

Add the vanilla extract and egg yolk to the butter mixture, mixing until well combined.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.

Using a cookie scoop or tablespoon, drop rounded balls of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Gently press each cookie ball down slightly with the palm of your hand, then sprinkle a small pinch of flaky sea salt on top of each cookie.

Bake in the preheated oven for 12-15 minutes, or until the edges are lightly golden.

Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.