Preheat oven to 350 degrees. In bowl cream together butter, shortening, and sugar. Stir in the eggs and vanilla. Combine the flour, baking powder and salt, stir into 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 two inches apart.
Bake cookies 10 to 12 minutes in oven until bottom is light brown.