Cream together the softened butter and powdered sugar until light and fluffy, about 2-3 minutes.
Gradually add the flour and salt to the butter mixture. Mix on low speed until just combined.
Add the egg yolks to the mixture and blend until well incorporated.
If the dough feels too dry, add cold water one tablespoon at a time until you achieve a soft, workable consistency.
Cover the dough with plastic wrap and refrigerate for at least 30 minutes.
Preheat your oven to 180°C (350°F).
Scoop out tablespoon-sized portions and roll them into balls. Place them on a lined baking sheet.
Using your thumb or a small spoon, gently press down in the center of each dough ball to create an indentation.
Spoon a small amount of apricot jam into each thumbprint.
In a small bowl, whisk together 1 egg yolk and 1 tablespoon of milk. Brush this mixture over the edges of each cookie.
Bake the cookies for 12-15 minutes or until the edges are lightly golden.
Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack.
