Pre-heat oven to 350 degrees. Cream butter, adding sugar gradually. Mix thoroughly. Add eggs one at a time, beating well. Stir in vanilla. Mix the flour, baking powder and salt together. Add to the butter mixture. Knead thoroughly. Chill dough. Roll out on a floured board unti thin. Cut out cookies. Bake for 10 - 12 minutes or until light golden brown. Cool thoroughtly before storing.