01 - Preheat oven to 350°F and line a baking sheet with parchment paper.
02 - In a large bowl, cream together butter and sugar until light and fluffy.
03 - Beat in egg yolk and vanilla extract until fully incorporated.
04 - Gradually mix in flour and salt until just combined, being careful not to overmix.
05 - Roll dough into 1-inch balls and place on prepared baking sheet, spacing 2 inches apart.
06 - Using thumb or back of spoon, gently press an indentation into center of each ball.
07 - Fill each indentation with about 1/2 teaspoon of lemon curd.
08 - Bake for 10-12 minutes, until edges just begin to turn golden.
09 - Let cool on baking sheet for 5 minutes, then transfer to wire rack to cool completely.
10 - Dust cooled cookies with powdered sugar before serving, if desired.