01 - Preheat oven to 350°F and line two baking sheets with parchment paper.
02 - In a large bowl, cream softened butter and granulated sugar until light and fluffy using electric mixer or whisk.
03 - Beat in egg yolk and vanilla extract until fully incorporated into mixture.
04 - Add salt and flour, mixing until just combined. Avoid overmixing to prevent tough cookies.
05 - Scoop tablespoon-sized portions, roll into balls, and place on prepared baking sheets spaced 2 inches apart.
06 - Press thumb or back of small spoon into center of each dough ball to form a well.
07 - Fill each indentation with 1/2 teaspoon of flower jam, being careful not to overfill.
08 - Bake for 12-15 minutes until edges are just turning golden brown.
09 - Let cookies cool on baking sheets for 5 minutes before transferring to wire rack. Dust with powdered sugar once completely cooled, if desired.