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