Preheat oven to 350 degrees and line 2 baking sheets with parchment paper then set aside. Cream butter and sugar together with a hand mixer until light and fluffy. Add egg yolk and mix well.


Slowly add the flour and continue to mix until blended. With a spoon, form cookie dough into small balls. Place on the prepared cookie sheets. 


Using your thumb make an indentation in each cookie and fill with lemon curd. Place pans in the oven and bake for 18 minutes, checking to make sure the edges of the cookies are slightly golden.