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 together until light and fluffy, approximately 2-3 minutes.
03 - Mix in egg yolk and vanilla extract until fully incorporated into the butter mixture.
04 - Add salt and flour to the mixture, stirring until just combined. Avoid overmixing to prevent tough cookies.
05 - Scoop tablespoon-sized portions of dough and roll into smooth balls. Arrange on prepared baking sheets with 2 inches of space between each cookie.
06 - Press your thumb or the back of a small spoon into the center of each dough ball to create a well for the jam filling.
07 - Spoon approximately 1/2 teaspoon of flower jam into each indentation, being careful not to overfill.
08 - Bake for 12-15 minutes until edges are lightly golden. Centers should remain set but not browned.
09 - Let cookies rest on baking sheets for 5 minutes before transferring to a wire rack. Dust with powdered sugar once completely cooled.