Arrange graham crackers, touching, to cover the entire rimmed baking sheet, cutting pieces as necessary. Melt butter and brown sugar slowly in a saucepan. When melted, add the entire amount of chopped pecans to the mixture and spoon contents over the graham crackers as evenly as possible. Bake at 350 degrees for 11 to 13 minutes. Allow cookies to cool before cutting and removing them from the pan. Store in an airtight container.