In a large mixing bowl, cream together the softened unsalted butter and granulated sugar using an electric mixer for about 3-4 minutes until light and fluffy.

Add in the egg yolk and vanilla extract, mixing until fully combined and smooth.

Gradually sift in the all-purpose flour and a pinch of salt, mixing gently until a soft, slightly sticky dough forms.

Using a tablespoon, scoop out portions of dough and roll into smooth balls, then place on a parchment-lined baking sheet.

Flatten each ball lightly with your palm and sprinkle with extra sugar.

Cover the baking sheet with plastic wrap and refrigerate the dough for at least 30 minutes.

Preheat your oven to 350°F (175°C) and bake for 12-15 minutes until the edges are lightly golden.

Allow the cookies to cool on the baking sheet for about 5 minutes before transferring to a wire rack.