Preheat the oven to 350°F (180°C). Line two large baking sheets with parchment paper or silicone mats and set aside.
In a large bowl or in the bowl of a stand mixer fitted with the paddle attachment, beat the softened butter and granulated sugar together for 1 to 2 minutes until smooth and well combined. Mix in the egg yolks, vanilla extract, and salt until fully incorporated.
1 cup unsalted butter, ⅔ cup granulated sugar, 2 large egg yolks, 1 teaspoon pure vanilla extract, ¼ teaspoon salt
Gradually mix in the all-purpose flour until the dough comes together. It may look crumbly at first—keep mixing until it forms a smooth dough.
2 ⅓ cups all-purpose flour
Scoop about 1 tablespoon of dough per cookie and roll each portion into a smooth ball. For a touch of sparkle, roll the dough balls in granulated sugar before placing them on the prepared baking sheets.
Use your thumb or the end of a wooden spoon to make a small indentation in the center of each cookie. Spoon about ½ teaspoon of strawberry or apricot jam into each indentation.
½ cup strawberry or apricot jam
Bake for 12 to 14 minutes, or until the cookies are set and the bottoms are lightly golden.
Allow the cookies to cool on the baking sheet for about 10 minutes, then carefully transfer them to a wire rack to cool completely.