Mix together first four ingredients until very fluffy, scraping sides of bowl occasionally. Slowly beat in flour and baking powder until well-combined. Cover dough and refrigerate for an hour.
Roll chilled dough out on floured board or counter until desired thickness. Cut with cookie cutters. Place on parchment-lined baking sheets. Bake at 400 degrees for 5-7 minutes or until just set and edges begin to brown. Don't overbake!
Remove to cooling racks and frost when completely cooled.
To make frosting: Beat together all frosting ingredients until fluffy. Add food colouring as desired. To create multiple colours, divide frosting into individual bowls and add food colouring as desired.
Store iced cookies between waxed paper in tightly sealed container or set out on festive platters and watch them disappear!
