Preheat the oven to 350° F.
In the bowl of a stand mixer, cream together the butter and granulated sugar for a full 2 minutes.
Scrape the sides of the bowl and add in the egg and vanilla, mixing until mostly combined.
Add the flour and baking powder. Mix until a soft dough forms. (This may take a minute, just trust the process! it will come together).
Feel the cookie dough in your hand, it should feel soft, like play-doh. If it is too dry and stiff, add 1 tsp of water at a time until getting that soft consistency.
Turn the dough out onto a floured surface - using a rolling pin slowly roll the cookie dough out until desired thickness. The cookies will not spread or rise while baking. Roll out to how thick you want your finished cookie to be.
Use desired Christmas cookie cutters to cut the cookie dough. Place cut out cookies on an ungreased cookie sheet or a parchment lined cookie sheet.
Wet hands with water and then gather the scraps together and repeat, rolling and cutting.
Bake at 350° F for 7-10 minutes- depending on size and shape. Pull them out of the oven once they have puffed up slightly and no longer look wet and glossy in the center. Do not let the cookies turn brown.
Allow the cookies to cool on the pan for 5-10 minutes before transferring to a cooling rack.
While the cookies are cooling, make the frosting.