Whisk flour, baking powder and salt. Beat butter and sugar until creamy. Beat in egg and vanilla, then mix in dry ingredients until combined. Divide into 2 disks, wrap and refrigerate 1 hour.

Heat oven to 350°F and line baking sheets. Roll dough between parchment to 1/4 inch thick. Cut out snowflakes and place 1 inch apart. Chill cut shapes 15 minutes.

Bake 10–12 minutes, until edges are set and just starting to turn pale gold. Cool 5 minutes on the sheet, then transfer to a rack and cool fully.

Tint some icing blue if desired. Decorate cooled cookies with icing and sprinkles. Allow icing to dry according to the package before stacking.