01 - Preheat oven to 350°F and line two baking sheets with parchment paper.
02 - In a large bowl, cream together softened butter and sugar until light and fluffy.
03 - Beat in egg yolk and vanilla extract until fully incorporated.
04 - Add salt and flour, mixing until just combined. Avoid overmixing to maintain tender texture.
05 - Scoop tablespoon-sized portions and roll into balls. Place on prepared baking sheets, spacing 2 inches apart.
06 - Using your thumb or the back of a small spoon, press a well into the center of each dough ball.
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, then transfer to wire rack. Dust with powdered sugar once completely cooled, if desired.