Since it’s getting to be picnic weather, it seems like a great time to pull out this Great American (really North American) classic. As a rule I don’t get terribly excited about cookies. With a few notable exceptions, the standard round “drop” cookie leaves me rather cold. Bar cookies are an entirely different matter. They’re like giant sheets of pie, cut up into individual little portions. And who couldn’t love a thing like that? Since bar cookies are among the easiest of all sweets to make, I plan on doing several different kinds this week, starting with a decadent classic: the seven layer bar. Oh, this is going to be fun.