01 - Preheat oven to 350°F and line two baking sheets with parchment paper.
02 - In a large bowl, beat softened butter and granulated sugar until light and fluffy, approximately 2-3 minutes.
03 - Mix in egg yolk and vanilla extract until fully incorporated into the butter mixture.
04 - Add salt and flour, mixing until just combined. Avoid overmixing to prevent tough cookies.
05 - Scoop tablespoon-sized portions of dough and roll into smooth balls. Arrange on prepared baking sheets, spacing 2 inches apart.
06 - Press your thumb or the back of a small spoon into the center of each dough ball to form a deep indentation.
07 - Spoon approximately 1/2 teaspoon of flower jam into each well, taking care not to overfill.
08 - Bake for 12-15 minutes until edges are just beginning to turn golden brown.
09 - Let cookies rest on baking sheets for 5 minutes, then carefully transfer to a wire rack to cool completely.
10 - Dust cooled cookies lightly with powdered sugar before serving, if desired.