01 - Preheat the oven to 350°F and line two baking sheets with parchment paper.
02 - In a large bowl, cream together the softened butter and sugar until light and fluffy using an electric mixer or whisk.
03 - Beat in the egg yolk and vanilla extract until fully incorporated.
04 - Add the salt and flour, mixing until just combined. Avoid overmixing to prevent tough cookies.
05 - Scoop tablespoon-sized portions of dough and roll each into a ball. Place on prepared baking sheets, spacing them about 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 approximately 1/2 teaspoon of flower jam.
08 - Bake for 12–15 minutes, or until the edges are just turning golden.
09 - Let cookies rest on baking sheets for 5 minutes before transferring to a wire rack. Dust with powdered sugar once completely cooled, if desired.