In a large mixing bowl, combine softened unsalted butter and granulated sugar. Using an electric mixer, beat on medium speed for about 5–7 minutes until the mixture is pale and fluffy.

Introduce one whole egg and 1 teaspoon of vanilla extract to the creamed mixture. Continue to mix on low speed until everything is well incorporated and smooth, about 1–2 minutes.

In a separate bowl, whisk together 2 cups of all-purpose flour, 1 teaspoon of baking powder, and 1/2 teaspoon of sea salt.

Gradually add the dry ingredients to the wet mixture, mixing gently until a soft dough forms.

Wrap the dough tightly in plastic wrap and refrigerate for at least one hour.

Once chilled, flour a clean surface and roll out the dough to about 1/2 inch thickness. Cut the dough into discs or your desired shape.

Transfer the cut cookies onto a parchment-lined baking tray, spacing them about an inch apart. Brush the tops lightly with a beaten egg yolk and score the tops with a fork.

Preheat your oven to 350°F (175°C) and bake the cookies for 15–18 minutes.

Allow the cookies to cool slightly on the tray for about 5 minutes, then transfer them to a wire rack. While still warm, sprinkle a pinch of flaky sea salt on top.