Preheat the oven to 350°F (180°C). Line a baking sheet with parchment paper.
Add the softened butter and sugar to a mixing bowl. Beat until creamy and well combined.
Add 1 egg yolk and vanilla extract. Mix until smooth.
Add the flour and mix just until a soft dough forms.
Shape the dough into a ball, wrap it, and chill for 30 minutes.
Roll the dough on a lightly floured surface to about 1/4 inch thick.
Cut the dough into round cookies and place them on the prepared baking sheet.
Mix the second egg yolk with 1 teaspoon milk. Brush a thin layer over the tops of the cookies.
Use a fork to gently score lines on top of each cookie.
Bake for 12 to 15 minutes, or until golden on top and lightly browned around the edges.
Let the cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.