Isabel's Holiday Cutout Sugar Cookies

In the bowl of an electric mixer fitted with a flat beater, beat together the butter and sugar on medium speed until light and fluffy, about 4 minutes.
Beat in the egg yolks one at a time, beating well after each addition.
Cut the vanilla bean in half lengthwise and, using a small, sharp knife, scrape the seeds into the butter mixture. Mix well.
In a sifter, combine the flour, backing powder and salt. Sift the flour mixture directly onto the butter mixture. Reduce the speed to low and beat until well mixed.
Divide the dough into 4 equal portions. Shape each portion into a ball, then flatten the balls into disks. Wrap in plastic and refrigerate overnight. (The dough can be prepared up to 3 days ahead.) Let it soften slightly at room temperature before continuing.
Position on a rack in the upper third of an oven and preheat to 350 degrees. Butter 2 large baking sheets.
On a lightly floured work surface, roll out a dough disk ¼ inch thick. Using cookie cutters, cut out desired shapes. Transfer the cutouts to the prepared baking sheets. Gather up and reroll the scraps and cut out more cookies. Repeat with the remaining dough disks.
Bake until the cookies are golden on the edges, about 8 minutes. Transfer the cookies to wire racks and let cool completely. Decorate the cookies as desired with colored sugars and decorating pens.
Store in an airtight container at room temperature for up to 1 week. Makes 24 to 30 cookies depending on cutter size.