Preheat oven to 350℉. Line baking sheet with parchment paper. Cream butter and powdered sugar in mixer for about 3-4 minutes. Add egg yolk, lemon juice, zest, and salt and mix until combined. Mix in flour on low speed just until you notice small clumps to form. Form dough into 1 inch dough balls and place dough balls on cookie sheet 1 inch apart from each other. Using your thumb, dip it in flour and then press down in middle of cookie enough to fill with lemon curd.

Bake cookies at 350℉ for 18-20 minutes or until just golden on the outside. Remove cookies from oven. Add lemon curd to cookies as soon as removed from the oven. May serve immediately or return cookies to oven for another 2-4 minutes in order to set the curd. Dust cookies with powdered sugar just prior to serving.

Notes: If making cookies ahead of time, wait to add lemon curd until ready to serve.