Preheat oven to 350 degrees.
Line 1-2 cookie sheets with parchment paper; set aside.
In a medium bowl, mix the GF Flour Mix, Baking Powder and Salt; set aside.
Using a Stand Mixer, combine the Butter and Sugars until smooth and creamy.
Next, add the Egg, Vanilla, Lemon Zest and Lemon Juice to the Butter-Sugar mixture, blending well.
Add the Flour Mixture, 1/2 cup at a time, to the dough, mixing on the Low setting until just combined.
Using a small cookie scoop (or spoon and rolling the dough into balls), scoop out the cookie dough onto the prepared cookie sheets, placing them 2" apart. Using the palm of your hand or the bottom of a glass, slightly flatten each cookie to form disks.
Bake for 12-15 minutes, depending on your oven. I bake mine for 14-15 minutes, because I prefer these cookies to be slightly crunchy, like the original Sunshine recipe.
Let the cookies cool on the sheets for about 5 minutes.
Carefully toss 3-4 cookies at a time in the powdered sugar mixture, coating each cookie well.
Place the powdered cookies on a cooling rack to continue cooling.
Enjoy!