1 Mix the fats, sugar, and extracts: In the bowl of a stand mixer fitted with the paddle attachment, place the butter, shortening, sugar, baking powder, vanilla and peppermint extract and salt.
Mix on slow speed until most of the ingredients are blended, then increase to medium speed and mix until the butter is creamy and clings to the side of the bowl, about 2 minutes. Scrape down the sides of the bowl halfway through mixing and then afterwards.
2 Add the eggs and flour: Add the egg and egg white to the bowl and mix until incorporated. Scrape down again.
Add the flour and turn the mixer to low. Once most of the flour has been absorbed, increase the speed to medium low until no dry flour remains. Scrape down the sides of the bowl once or twice to make sure the dough is completely homogenized.
3 Prepare dough to chill: Scrape out the dough onto some plastic wrap. Pat the dough…