- With the rack in the middle position, preheat the oven to 190 °C (375 °F). Lining one to two baking sheets with parchment paper. You'll do about four batches (your sheet filled with cookies x 4 in the oven).
- In a bowl, combine the flour, cornstarch, baking powder, and salt. Set the bowl aside.
- In another bowl, cream the butter with the sugar and vanilla using an electric mixer for about 3 minutes. Add the eggs, one at a time, and continue beating until smooth. At low speed or with a wooden spoon, combine with the dry ingredients that you have put aside.
- With your hands, shape the dough into two discs. Cover them with plastic wrap and put them in the refrigerator for about 1 hour.
- On a floured work surface, roll out the dough to about 3 to 5-mm (1/8 to 1/4-inch) thick. Cut out cookies, using a cookie cutter of your choice. Spread the cookies of the same size on the same sheet, because the cooking time may vary.
- Bake, one sheet at a time, from 8 to 10 minutes or until the edges are lightly golden brown. Let them cool.
- In a bowl, gently beat the egg white and icing sugar with an electric mixer for about 2 minutes or until it forms soft peaks. You can color the icing the color of your choice.
- Using a pastry bag fitted with a small plain tip, decorate your cookies.
Do not throw out the leftover dough. You can roll it and make more cookies.