This take is hot out of the mini oven:
Isn't the point of a traybake to make a large cake that can be easily served up in squares or rectangles on a picnic or party? Doesn't really require a plate and a cake fork - more of a hold in your napkin type of cake? Typically found at potlucks, school fetes, parties, etc.?
Also, applesauce works well in many vegan recipes. I have no issue with it. The only issue I do have is that it comes from US recipes and an American applesauce is a very different beast to a UK applesauce. It is much more like the apple puree you can buy here in pouches or pots for babies. It's sweeter than UK applesauce, it's not chunky and it never, ever contains vinegar, cider or starch, which a lot of shop bought UK versions use. It's because applesauce in the US is eaten as a snack on its own or mixed with yoghurt or on potato latkes or sometimes pancakes, whereas UK applesauce is a condiment to many meat dishes.
Anyway, why am I mithering on about it? Because in baking it will make a huge difference whether your applesauce is smooth or chunky, whether there is vinegar and starch in it or not and what the sugar content is. However, I assume that her prune concoction would always be disgusting, so I guess the old adage remains true - applesauce is applesauce.