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 together until light and fluffy, approximately 2-3 minutes.
03 - Mix in egg yolk and vanilla extract until fully incorporated and smooth.
04 - Add salt and flour to the mixture, stirring until just combined. Avoid overmixing to prevent tough cookies.
05 - Sop tablespoon-sized portions of dough and roll into smooth balls. Arrange on prepared baking sheets with 2 inches of spacing between each.
06 - Press your thumb or the back of a small spoon into the center of each dough ball to create 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 lightly golden. Centers should remain pale.
09 - Let cookies rest on baking sheets for 5 minutes, then transfer to wire rack to cool entirely.
10 - Lightly dust cooled cookies with powdered sugar using a fine-mesh sieve for an elegant finish.