Whisk together the flour, baking powder, and salt; set aside.
Beat the butter and sugar together until light and fluffy.
Beat in the egg, then mix in the vanilla.
Gradually mix in the dry ingredients until a soft dough forms.
Divide the dough in half, flatten, and refrigerate for at least 1 hour.
Roll to 1/4-inch thickness and cut into snowflake shapes.
Bake at 350°F for 8 to 10 minutes, until edges are just golden.
Cool completely, then pipe royal icing in a snowflake pattern and add glitter or sugar while wet.