Whisk together the flour, baking powder, and salt in a small bowl. Set aside.
Cream the butter and sugar in a bowl (use a plastic or wooden spoon or spatula). Mix until well combined. Add whipped egg and vanilla. Mix until well combined (3-4 min.).
Slowly incorporate the flour mixture into the butter mixture. Mix until well combined but do not over mix dough.
Drop dough by the tablespoonful onto cookie sheet 1/4" apart. Use your first two fingers and press cookies down at least 1/2 " - 1/4" thick. Do not make them too thin.
Bake for 10-12 minutes or until the cookies are lightly golden brown. (Place cookie sheet in the oven on the middle rack.).
Let cookies cool completely. If you are using colorful sugars or sprinkles, feel free to top your cookies while they are still warm, not hot. Top with frosting or icing after cookies are completely cooled. You will want to refrigerate them with the frosting on top to allow the frosting to properly set.