Lemon Shortbread Sandwich Cookies
Shortbread Cookie Dough:
In a bowl, whisk together the flour, powdered sugar and salt. Scatter the cold butter pieces over the flour, and using a pastry cutter, cut the butter into the flour until you have coarse crumbs with visible chunks of butter throughout. Add the egg yolk stirring into the flour and butter with your fingers. Work the dough with your fingers to incorporate the moisture into the flour. (The dough will appear very dry, and you might think it doesn't have enough liquid, but don't worry, it will come together.) After 2-3 minutes of working the dough, it should start to hold together enough so that you can gather it into a ball. Add the ice water, a little at a time, just to finish bringing the dough together so that you can roll it out.
Shape the dough into a disk and set on a piece of parchment paper, lightly floured. Place another piece of parchment paper on top of the dough. Roll the dough out to 1/4 inch thick. Use a cookie cutter to cut as many cookies as you can; transfer the cookies to a baking sheet lined with parchment or a silpat, placing the cookies 1 inch apart. Gather up the dough scraps, roll them out again, and cut more cookies, continue rolling and cutting until you've used up all the dough. You should be about to cut about 3 dozen cookies, depending on the size of your cookie cutter/s.
Freeze the cookies on the baking sheets for 45 minutes to an hour. This will help ensure that they hold their shape and do not spread out during baking.
Preheat the oven to 350. Bake the cookies (straight from the freezer) for 12 minutes, just until a very pale golden (the cookies do not rise or spread). Cool completely on a wire rack.
If desired, drizzle with a little melted chocolate.
Yields about 1 1/2 dozen filled cookies or 3 dozen cookies without filling.