Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheets.
Cream together the butter and sugar. Beat the egg, and blend into the butter and sugar. Mix in the lavender flowers, baking powder, vanilla, salt and the flour. Drop batter by teaspoonfuls onto cookie sheets.
Bake 15 to 20 minutes, or until golden. Remove cookies to cooling racks, and sprinkle with decorative sugar and additional lavender flowers if desired.