Whisk flour, baking powder and salt together in medium bowl.
In a food processor, process sugar and lemon zest until finely ground, about 30 seconds. Add egg and yolk, butter, oil, vanilla, and lemon juice and process until pale and thickened, about 30 seconds. Stir egg mixture into flour mixture until incorporated. (It will be sticky) Cover bowl with plastic wrap and refrigerate for at least 1 hour.
Preheat oven to 350º and line baking sheets with parchment paper. Place confectioners’ sugar in a small bowl.
Form into balls using a small ice cream scoop. Toss in confectioners sugar to coat and place on prepared pans. Bake until cracked and set on top but moist within cracks, 10-12 minutes depending on the size of the cookies.
America’s Test Kitchen Best Ever Christmas Cookies