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.
03 - Mix in egg yolk and vanilla extract until fully incorporated.
04 - Add salt and flour, mixing until just combined. Avoid overmixing to prevent tough cookies.
05 - Scoop tablespoon portions and roll into balls. Place on prepared baking sheets 2 inches apart.
06 - Press thumb or back of small spoon into center of each dough ball to create a deep indentation.
07 - Fill each well with 1/2 teaspoon of flower jam, being careful not to overfill.
08 - Bake for 12 to 15 minutes until edges are just turning golden brown.
09 - Let cookies rest on baking sheets for 5 minutes, then transfer to wire rack to cool fully.
10 - Dust cooled cookies with powdered sugar before serving.