In a mixing bowl, whisk together the flour and salt.
In a separate bowl with an electric mixer (using the paddle attachment), beat the butter and sugar until well combined.
Add the egg yolks and vanilla extract, and mix on low speed. Gradually add the flour mixture and mix until everything is just combined.
Scoop about 1 tablespoon of dough at a time (24g), roll into balls, and place them on a flat surface. Press your thumb into the center of each ball to create an indentation.
Transfer the dough balls to plates, leaving a little space between them to prevent sticking. Chill in the refrigerator for 60 minutes.
Halfway through chilling, preheat the oven to 350°F (175°C). Once chilled, transfer the cookies to a baking sheet lined with parchment paper or a silicone mat, spacing them 2 inches apart. Keep any extra dough balls in the fridge until ready to bake.
Bake for 16 minutes, or until set. Immediately after removing from the oven, use the back of a teaspoon to press down the center of each cookie again, as the indentations may have flattened while baking.
Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.