My sister in law makes the hardest cookies I've ever had. She uses dark cookie sheets instead of shiney ones. Here is her recipe.
1 cup butter or margerine
1 cup white sugar
1 cup brown sugar
2 eggs
2 tsp. vanilla
3 cups flour
1 tsp. salt
1 tsp. baking soda
2 cups chocolate chips
Drop by rounded tsps. onto ungreased cookie sheets.
Bake at 375 for 8-10 minutes.