- With the rack in the middle position, preheat the oven to 180°C (350°F). Line 2 cookie sheets with parchment paper.
- In a bowl, combine the flour, baking powder and salt. Set aside.
- In another bowl, cream the butter, sugar and vanilla with an electric mixer. Add the egg and beat until creamy.
- Using a wooden spoon, stir in the dry ingredients. Shape the dough into a log. Cut off 1/3 of the dough and wrap in plastic wrap. Refrigerate for 20 minutes.
- Meanwhile, cut the rest of the log into 6 to 8 rounds. In a bowl, combine 1 round with 1 drop of colouring using a spoon or gloved hands. Repeat with remaining dough and colours (be sure to wipe the bowl clean between colours). Shape the coloured portions into discs, transfer to a plate and cover with plastic wrap. Refrigerate for 20 minutes.
- On a floured surface, roll the uncoloured dough to a thickness of about 3 mm (1/8 inch). Using boy- and girl-shaped cookie cutters about 13-cm (5 1/4-inch) tall, cut out 4 cookies. Arrange on a cookie sheet. Roll out the coloured dough and use the same cookie cutters to cut into cookies. Cut the coloured cookies into articles of clothing (pants, dresses, skirts, shirts, caps, mittens, belts, etc.).
- Bake until the cookies start to brown slightly on the bottom, 7 to 10 minutes depending on size. Let cool on the cookie sheet.
- In a bowl, beat the egg white and sugar with a whisk or electric mixer until smooth. Add water as needed.
- Using a small spatula or a pastry bag fitted with a small plain tip, help children “glue” articles of clothing on the large cookies with royal icing. If desired, pipe or spread additional icing in decorative patterns on the dressed cookies. Let dry for 30 minutes.