Cream butter, shortening, and sugar using an electric mixer. Beat in eggs.
In a separate bowl whisk flour, cream of tartar, baking soda, and salt together.
Combine dry ingredients with butter/eggs mixture.
Scoop cookies, using a medium cookie scoop, on cookie sheets lined with parchment paper. I usually bake 6 cookies per sheet.Bake for 10 minutes.
Allow cookies to cool for 3 minutes before transferring to wire racks.
Spread cooled cookies with a thin layer of lemon curd and sprinkle with powdered sugar.Store cookies in an airtight container or cover in plastic in the refrigerator.
Video
Notes
If you prefer to not use shortening you can use butter instead. The texture of the cookie will be slightly different, but still delicious.