In my kitchen, I have a small collection of cookbooks that I consider prized possessions. One of them, the classic Betty Crocker Cookbook, was a wedding gift and, trust me, it’s seen more than its share of splatters and dog-eared and ripped pages. And I wouldn’t part with it for anything. Another features 100 things to do with an ordinary cake mix. It is fabulous—or I should say it used to be. Here’s the problem: About five years ago, cake mix manufacturers got the bright idea to shrink the contents of a standard cake mix rather than increase the price. Sneaky, right? And what a terrible decision that was. What used to be the standard 18.25 ounce cake mix suddenly shrunk to 15.25 ounces. Have you noticed this? That might not be a problem if you’re using that cake mix to make the cake according to the back-of-the-box instructions, which …