01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, beat butter and sugar until light and fluffy.
03 - Mix in egg yolks and vanilla extract until well combined.
04 - Add flour and salt; mix until soft dough forms.
05 - Roll tablespoon portions into balls. Place 2 inches apart on baking sheets.
06 - Press thumb or small spoon into center of each ball to make a well.
07 - Fill each indentation with 1/2 teaspoon jam.
08 - Bake for 13–15 minutes until edges are lightly golden.
09 - Let cookies rest on baking sheet for 5 minutes, then transfer to wire rack.