Sunny Lemon Shortbread Cookies

1    c. sugar
16  T. unsalted butter, softened
2     t. vanilla extract
1/4  t. salt
2    c. flour

1½ c. sugar
6    T. cornstarch
¼    t. salt
½   c. freshly squeezed lemon juice (at least 3 lemons)
3        egg yolks, beaten
2    T. butter
1½ c. boiling water
2-3 T. lemon zest

Preheat oven to 350 degrees.
In a large bowl, cream together butter and sugar. Add vanilla, giving a quick mix. Add a little bit of flour at a time, mixing until smooth. Shape dough into 2 equal discs, wrapping separately in plastic. Chill for at least 1 hour.
In a saucepan, stir together the sugar, salt, and cornstarch. Then, add in the lemon juice and cook over medium low heat until smooth. Add the egg yolks and butter. Keep stirring constantly until it thickens more.  Add 1 1/2 cups boiling water and continue to cook for 2 to 3 minutes more. The mixture will thicken a lot. (Make sure there are not “scrambled egg bits” in the mixture. You can either put it through a strainer or use a spoon to scoop them out.  Stir in the lemon zest. OR purchase lemon curd to use instead.
Lightly grease a mini cupcake pan. Roll out the dough to about 1/4-inch thick and cut using a round flower-shpaed cookie cutter. Gently press cut out dough flowers into greased cupcake pan.  Fork each throughout on the bottom and sides to prevent them too much puffing . Then transfer to the freezer for 10 minutes before putting in the oven to bake for 8-10 minutes. Put a dab of lemon filling in the center of each cooking. Bake for an additional 5-8 minutes. Cool to room temperature, then transfer to the refrigerator to cool until completely set. Store chilled. When ready to serve, sprinkle with powdered sugar, if desired.

Tried a variation on a recipe from "The Love Nerds" blog, which was reminiscent of lemon bars in taste.  Sugar cookie dough wass rolled, cut into flowers that were pressed into a mini cupcake pan, baked, and filled with lemon curd.  (Apricot jam was substituted when jar of lemon curd ran out, but a number of other fillings would work, possible caramel or chocolate would be popular.)