01 - Preheat oven to 350°F and line two baking sheets with parchment paper.
02 - In a large bowl, cream softened butter and sugar until light and fluffy using electric mixer or whisk.
03 - Beat 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-sized portions and roll into balls. Place on prepared baking sheets, spacing 2 inches apart.
06 - Press thumb or back of small spoon into center of each dough ball to form a deep well.
07 - Spoon approximately 1/2 teaspoon flower jam into each indentation.
08 - Bake for 12-15 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 before dusting.
10 - Lightly dust cooled cookies with powdered sugar if desired.