Preheat your oven to 350°F. Line two baking sheets with parchment paper; set aside.
In a large bowl, whisk together the flour, baking powder, and salt.
In a stand mixer (or another large bowl and using a hand mixer), beat the butter until it's light yellow, smooth and creamy. This takes anywhere from 3 to 5 minutes. Don't skimp on this step!
Add the sugar, egg, and vanilla to the creamed butter and beat together on low until incorporated.
Slowly add the dry ingredients to the wet ingredients in the stand mixer and beat together just until combined. Be careful not to overmix.
Turn out the dough on a lightly floured surface and roll out until about ¼" to ½" thick. It's really up to you how thick you want your cookies to be. Thinner cookies will be crispy; thicker cookies will be softer.
Using snowflake cookie cutters, cut out cookies and place onto the prepared baking sheets.
Bake at 350°F for 10 to 12 minutes, just until the edges of cookies start to turn a light golden brown.
Remove the pans from the oven and allow the cookies to rest for a couple of minutes in the pan before transferring them carefully to a wire rack to cool completely.
Once the cookies are cool to the touch, decorate with royal icing.
Notes
Makes: This recipe makes a LOT of cookies! But the exact number depends on the size of your snowflake cookie cutters. I've been able to get about 4 dozen (48) 3"-4" snowflake cookies plus about a dozen smaller cookies from one batch. Again, this will greatly depend on your exact cookie cutters. Egg and butter: Make sure you bring both the egg and the butter to room temperature before using. Simply take them out of the refrigerator and place them on your countertop about 30 minutes before you start gathering the rest of the ingredients and start baking.Chill: This dough does not need to be chilled before baking. However, if your kitchen is warm or you are baking these on a warm day/in a warm climate, I do suggest chilling the dough in the refrigerator for a couple of hours before rolling out. Storage: Store unfrosted cookies in an airtight container at room temperature for up to 4 days, in the refrigerator for up to 5 days, or in freezer bags or containers the freezer for up to two months.