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

In a large bowl, cream together the softened butter and granulated sugar until light and fluffy, approximately 3 minutes.

Beat in the egg yolks, vanilla extract, and salt until well combined.

Gradually add the flour to the wet ingredients, mixing on low speed until a soft dough forms.

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

Using your thumb or the back of a small measuring spoon, press a deep indentation into the center of each dough ball.

Fill each indentation with approximately 1/2 teaspoon of strawberry jam.

Bake for 12 to 15 minutes, or until the edges are just beginning to turn golden brown.

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