In medium bowl, whisk flour, baking powder, salt. In large bowl, beat butter and sugar until smooth, 1 minute. Beat in egg, vanilla, rind, juice. On low, beat in flour mixture. Remove half of dough to bowl; tint green. Flatten each half of dough into 8-inch disk; wrap each in plastic. Chill 2 hours.Advertisement
Heat oven to 350 degrees F. On floured surface, roll out green dough, 1/8 inch thick. Cut out trees with 3-inch tree cookie cutter. Place on ungreased baking sheets. Gather scraps; reroll; cut out more trees. Repeat with white dough. Chill 10 minutes. Using 1/2-inch-round aspic cutter and flouring edge frequently, cut rounds from trees; put green circles in cutouts in white trees, and white circles in green trees.
Bake in 350 degree F oven until golden around edges, 10 minutes.
Mix sugar and juice. Brush on hot cookies; cool.