Into a mixing bowl, sift flour, baking powder and salt. Sift the mixture again.
In a separate bowl, combine the shortening sugar, egg, egg yolk, lemon juice, and lemon zest, and beat together. Add the flour mixture and beat together.
Refrigerate the dough overnight.
Preheat oven to 375 degrees F
Remove dough from refrigerator. Prepare your work area with flour.
Tear off a baseball-sized piece of dough, and place the remainder back into the refrigerator.
Flour the top of the dough. Use a rolling pin to roll out the dough to about 1/8" thick.
Cut cookies with a cookie cutter place them on a greased cookie sheet.
Bake at 375 degrees for 12-15 minutes. Repeat until all of the dough has been used.
Cool completely. Dust with powdered sugar.