In a large bowl, cream together softened butter and granulated sugar until light and fluffy.

Add the egg yolk and vanilla extract, mixing until fully combined.

Gradually add the flour and salt to the butter mixture, stirring until a soft dough forms.

Wrap the dough in plastic wrap and refrigerate for at least 30 minutes to firm up.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.

Roll the chilled dough into 1-inch balls and place them on the prepared baking sheets, spacing them about 2 inches apart.

Use your thumb or the back of a spoon to press an indentation into the center of each ball.

Spoon a small amount of jam into each indentation, being careful not to overfill.

Bake for 10–12 minutes, or until the edges are lightly golden.

Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

Optional: Dust the cooled cookies with powdered sugar for a decorative finish.