Preheat the oven to 350º F.
In a bowl, add your dry cookie ingredients and whisk to blend.
Put the wet ingredients into a smaller bowl and whisk to blend.
Pour the wet ingredients into the dry ingredients and mix.
Wrap the dough in plastic wrap.
Refrigerate the cookie dough for 45 minutes.
Remove from the refrigerator and place the dough on wax paper. Place another piece of wax paper on top.
Use a rolling pin to roll out the dough until it is ½ inch thick.
Take your favorite cookie cutters and cut out cookies.
Place the cut out cookies on a parchment-lined cookie sheet and bake for 8-10 minutes.
Remove from the oven and cool on a cooling rack.
Make the icing!
Using a standing mixer, add powdered sugar, egg whites, cream of tartar and salt.
Turn the mixer on SLOW. (If you turn it on too fast, it will explode sugar everywhere!)
Slowly mix the icing for 9 minutes until it becomes somewhat fluffy and thick.
Decorate your cookies, don't forget to let each color icing dry before adding another color, otherwise, the colors can run together.