Snowflake Sugar Cookies

Sift in the confectioners' sugar, beat on low at first so it doesn't fly everywhere, then increase the speed to high and beat until very light and fluffy, about 2 to 3 minutes.

Add the vanilla extract and beat momentarily to incorporate. Stop and scrape down the sides of the bowl.

Add the flour, baking powder, salt, and beat to just incorporate, don't overmix. The dough will be very thick.

Add the milk, 1 tablespoon at t time, mixing briefly after each tablespoon, until a thick but smooth dough can come together. 
Notes - You may not need all of the milk, so don't add it if you don't need it. Stop adding it after your dough has come together. I doubt you will need more milk than called for, but perhaps if you have a very thick or crumbly dough (remember not to over-measure/pack in the flour when you're adding it in the previous step to prevent an overly dry dough) add a bit more milk until your dough comes together.

Take the dough out of the mixer, divide it in half (approximately), pat the dough into large thick disc shapes, cover with plastic wrap, and refrigerate for at least one hour, or overnight, to chill.

After the dough has chilled at least 1 hour and you're ready to rol it out, preheat the oven to 350F.

Remove the dough from the fridge, generously flour a clean countertop so the dough doesn't stick, and roll the dough out to approximately 1/8-inch thick. 
Tip - If you've been chilling the dough for longer than about 3 hours (especially if you chilled it overnight) give it about 15 minutes at room temp before you attempt to roll it out.

Using snowflake cookie cutters (or your favorite shape of cutters), cut out snowflake shapes, wasting as little dough as possible and cutting as closely as possible to form the snowflakes. 
Tips - You can ball up and then reroll your scraps of dough. However, I only reroll once. After that the dough gets a bit overworked and isn't at its best. Make whatever shape of circular cookie(s) you'd like for the final bits of dough and call it a day is my advice..

Place the cut snowflakes on parchment paper lined or Silpat lined baking mats on baking sheets and bake for approximately 8 to 10 minutes. Baking time will vary considerably based on the size of your snowflakes (or other shapes of cookies), oven and climate variances, etc. Pay close attention to your cookies in your oven, and pull them when the edges are just barely turning golden brown. Cookies will continue to set, firm up, and darken in color as they cool. 
Tips - I suggest baking one tray of cookies at one time, on the center oven rack, and rotating once midway through baking for best results.

Allow cookies to cool on the baking sheets for about 5 to 10 minutes, or until they've firmed up enough to carefully transfer to wire racks to cool completely.

Frosting - Read the 'Notes' at the bottom of this post to see what frostings you can buy or make. Spread a thin layer of frosting using a butter knife or small spatula over the surface of every cookie. Fun Tip - You can color the frosting red, green, or another color of your choice with food coloring if you'd like.

Spread a thin layer of frosting using a butter knife or small spatula over the surface of every cookie.

Piping- To pipe the frosting you've made, transfer it into a pastry bag (or the tip of your choice) onto the bag, and begin to pipe small stars over the surface of every cookie.

As desired, add sprinkles to the top of each cookie.  Fun Tip - Feel free to use Christmas colored sprinkles, or whatever color and type of sprinkles you'd like.

Shortcut Frosting - The third and final option for frosting is to use another favorite store bought frosting like buttercream. You cannot pipe the frosting, so just spread it on the cookies with a butter knife or small spatula, and add sprinkles as desired. 

Storage - The vanilla whipped cream frosted cookies need to be stored airtight in the fridge where they will keep for 3 to 4 days.
If you use homemade vanilla buttercream, you can feel confident leaving them airtight at room temp for up to 5 days or in the fridge for up to 1 week.
If you use store bought frosting the cookies will keep airtight at room temp for up to 1 week.