Mix all the dry ingredients in a bowl: flour, cornstarch, sugar, salt, vanillin and baking powder.

Bring the water and vegetable oil to a boil and pour into the flour mixture. Stir with a spoon, and once it cools slightly, knead the dough by hand.

Wrap the dough in plastic wrap and refrigerate for 15 minutes.

Roll the dough out very thin and cut cookies with a cutter. Poke holes with a fork or skewer - though this step isn't strictly necessary.

Bake in an oven preheated to 190-200 °C for 7-10 minutes, until golden. All done - bon appetit!