01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, cream together butter and sugar until light and fluffy.
03 - Beat in egg yolks and vanilla extract until well combined.
04 - Add flour and salt. Mix until soft dough forms.
05 - Scoop tablespoon-sized portions, roll into balls, and place 2 inches apart on prepared baking sheets.
06 - Using thumb or back of small spoon, gently press indentation into center of each dough ball.
07 - Fill each indentation with about 1/2 teaspoon of jam.
08 - Bake for 13-15 minutes, or until edges are lightly golden.
09 - Allow cookies to cool on baking sheet for 5 minutes before transferring to wire rack to cool completely.