Whisk together the flour, salt, and baking powder in a medium mixing bowl.
In a separate bowl, cream the butter and sugar together using an electric mixer if you like.
Add the eggs, one at a time, and beat well. Then mix in the vanilla.
Add the dry ingredients (flour mixture) to the wet ingredients (butter mixture). Beat this until thoroughly blended.
Shape the cookie dough into a ball and place it in the fridge to chill for an hour.
When you are ready to bake the cookies, preheat the oven to 350 degrees. Allow the dough to rest at room temperature until it is soft enough to roll.
Spray your baking sheets.
Roll the dough out onto a well-floured surface. It should be about ¼ inch thick.
Use a lightly floured tree-shaped cookie cutter to cut out as many cookies as possible.
Place the cookies 1 ½ inches apart on the cookie sheets. Bake for 7-10 minutes or until small cracks appear all over the tops of the cookies. Watch them carefully and make sure to pull them out before the edges brown.
Place the cookie sheets on cooling racks and allow them to cool for 5 minutes before removing the cookies. Then allow the cookies to cool completely on cooling racks before decorating.
To make the frosting: cream the butter, beat in the powdered sugar a little at a time. Then mix in the vanilla. Only add enough milk to achieve the desired consistency and enough coloring to reach the desired color.
Pipe the frosting onto the trees using star shaped piping tip #98 starting at the base of the tree, then work your way up. Make sure to overlap the layers so you get the tree branches look.