Whisk the flour, baking powder and salt in a mixing bowl.
In a stand mixer fitted with the paddle attachment (or hand mixer), beat the butter, granulated sugar, and confectioners sugar on medium-high speed until light and fluffy, about 2 minutes. Scrape the bowl as needed.
Add the eggs and vanilla and mix until combined.
Gradually add the flour mixture and mix on medium-low speed until the dough just comes together.
Divide the dough into three even sized pieces.
Return one of the pieces of dough to the mixing bowl and add 5-10 drops of red gel food coloring to the bowl. Mix until the dough is evenly colored. Remove from the mixing bowl and clean the bowl and paddle attachment.
Place another piece of dough and add the green food coloring. Mix until the dough is evenly colored. Keep the third piece as is.
Flatten each ball of dough into a disc and wrap it in plastic wrap. Chill in the freezer for 20 minutes or in the fridge for 1 hour.
Roll out each disc of dough, one at a time, on a piece of parchment paper to create rectangles that are roughly the same size and shape. Stack the thin layers of dough on top of each other with white in the middle and red and green on the top and bottom. Trim the long sides so that the edges are even. The shorter ends can be trimmed later after you roll the dough into a log.
Using the parchment paper to assist you, carefully roll the dough into a tight log. Then wrap the dough in plastic wrap and chill in the fridge for at least 1-2 hours.
Once the dough is chilled, roll the log in nonpareils to coat the outside of each cookie. Press the dough firmly into the sprinkles to get them to stick and give good coverage. At this point, you can slice and bake the cookies, or wrap them up and store them in the fridge for up to 1 week to slice and bake as needed.
When ready to bake, preheat the oven to 350 degrees Fahrenheit and line a baking sheet with parchment paper.
Unwrap the roll of cookie dough and cut off the uneven ends, then slice into 1/4-inch cookies using a sharp knife and space them 1-2 inches apart on the parchment paper.
Bake for 10-12 minutes until set, then cool completely on a wire rack.