In a large mixing bowl, beat the softened butter and granulated sugar together with an electric mixer until light and fluffy, about 2-3 minutes.
Add the egg yolks, vanilla extract, and salt to the mixture. Beat until well combined.
Gradually add the all-purpose flour to the wet ingredients, mixing on low speed until just incorporated. Do not overmix.
Form the dough into a ball and wrap it tightly in plastic wrap. Refrigerate the dough for at least 30 minutes to make it easier to handle.
Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone baking mat.
Remove the chilled dough from the refrigerator. Roll the dough into 1-inch (2.5 cm) balls, roughly the size of a walnut. Place the dough balls about 2 inches (5 cm) apart on the prepared baking sheet. Use your thumb or the back of a rounded teaspoon to press a shallow indentation into the center of each dough ball.
Spoon about ½ teaspoon of your chosen fruit jam or preserves into each indentation. Be careful not to overfill, as the jam may overflow during baking.
Bake in the preheated oven for 12-15 minutes, or until the edges of the cookies are just beginning to turn golden. Remove from the oven and allow the cookies to cool on the baking sheet for 5 minutes. Transfer the cookies to a wire rack to cool completely.
Store any leftovers in an airtight container at room temperature for up to 1 week.