According to Jim Recap: Guess Who's Cooking Your Dinner?
Things are really heating up between Dana and Ryan, so Dana wants to cook him dinner to "seal the deal". There's just one problem - she can't cook. So she does what anyone would do, and she asks her sister to do it for her. She'll just pass off the cooking as her own. Naturally, Cheryl is trying to teach the kids that lying is wrong - that is, until Jim catches her when the kids mention that she is cooking dinner for Aunt Dana, then it's on.
As the big night gets ever closer, the pressure on Cheryl mounts. She keeps her mouth shut all the way until they are at the table eating - which I don't understand. If this massive meal takes two days of cooking, and Ryan is the only outsider there, why would they spend two days cooking at his place? Why not cook it elsewhere and invite him over? But I digress.
Finally, as they are just starting to get going on dinner, Cheryl cracks and she spills the beans about the dinner. Dana is about to erupt into tears, because Ryan had just asked her to marry him. But in the end, it all works out - he is much more impressed that she could manipulate the family like this than if she could have cooked, so the wedding is still on!
