Preheat oven to 325 ℉. Line a baking sheet with parchment paper or a silicone baking mat. Set aside.
In a large bowl using a hand held mixer, or a standing mixer with a beater attachment, cream the softened butter and granulated sugar until light and creamy, about 2-3 minutes.
Mix in the egg yolk, salt, and vanilla extract.
Add the flour and mix until just combined. Do not overmix the cookie dough.
Using an ice cream scoop or a large spoon, scoop about about 1.5 tablespoon balls of dough and roll in your hands until a uniform ball forms.
If desired, roll the ball in more granulated sugar.
Place the balls of dough on the prepared baking sheet, keeping them about 2 inches apart. Using your thumb, finger, or the back of a 1/2 teaspoon, gently press down in the middle of the ball of cookie dough.
If the dough cracks, gently press the cookie it back together with your fingers.
Bake in the preheated oven until the cookies just start to brown, about 12-15 minutes.
Remove the cookies from the oven and cool on the baking sheet for 5-10 minutes. Then remove the cookies by placing on a cooling rack to cool completely before filling.