Preheat oven to 350 degrees F (175 degrees C).
In a medium bowl, cream together the butter, shortening and sugar.
Stir in the eggs and vanilla. Combine the flour, baking powder and salt.
Stir into the creamed mixture until dough comes together.
Roll dough into walnut sized balls and roll the balls in sugar.
Place them on an unprepared cookie sheet about 2 inches apart.
Bake cookies 10 to 12 minutes in the preheated oven, until bottom is light brown.
Remove from baking sheets to cool on wire racks.