Preheat the oven to 180°C (350°F). Line a baking sheet with parchment paper. In a bowl, combine the flour, baking powder and salt. Set aside. In another bowl, cream the butter with the sugar and vanilla using an electric mixer. Add the egg and beat until the mixture is smooth. Using a wooden spoon, stir in the dry ingredients. On a lightly floured surface, roll the dough into a log. Cut into 24 slices and shape into balls. Place the icing sugar in a bowl. Roll the dough balls in the sugar, coating well. Arrange the balls on the baking sheet. Bake for about 15 minutes. Let cool. Dust the cookies with the remaining icing sugar.