I can shed some light on the weird jello-molds:

Gelatin was very difficult to produce before the industrial age, involving a process of taking 2 gallons of water per pound of bones, straining the remaining liquid through cheese cloth, then boiling the remaining liquid until it is 1/16th the volume. This required a lot of labor, and aspics, what today we would call jello molds were only eaten by the rich. They also needed to be cooled to be set properly, adding to the expense. Escoffier's The complete guide to the art of modern cookery has an entire section on how to make "gelatine" for aspics: https://babel.hathitrust.org/cgi/pt?id=pst.000061786981;view=1up;seq=70 This was a fancy food, and one can only hope that what came out of Escoffier's kitchen was far more enticing than what was made in suburban kitchens in the 50s-70s.

The industrialization of a gelatin for food use came slowly. There were several patents produced on this- IE US Patent 4084 in the mid 1800s. But it was not until the late 1800s when Charles Knox- of whose Knox brand of gelatin is still sold today- could create a truly granulated form of gelatin suitable for food use. By 1896 his wife had published a book on gelatin recipes: http://digital.lib.uiowa.edu/cdm/ref/collection/szathmary/id/604 Around this time Jello had been invented and marketed as well.

As to why they became a craze, its a bit harder to say, but I don't think it can be understated as to how influential Escoffier's cookbook was- it is essentially the mother of all modern cookbooks, and most "serious" cookbooks have a section on aspics- IE Julia Childs Mastering the art of French Cooking, Rombauer's The Joy of Cooking. The ease of setting gelatin based dishes with household refrigerators, cheap easy to use gelatin made available by manufacturing breakthroughs, the cachet of eating like fancy victorian era millionaires, and the very successful advertising campaigns for Jello lead to the rise of popularity of Jello desserts and later what we would call jello molds.

The ham and bananas and hollandaise follow a similar trend- "fancy" french cooking techniques (hollandaise) adapted to cheap highly available ingredients to a growing middle class with more time on its hands. Note that how that recipe uses a packet of hollandaise mix. Food like this was considered a mark of technological innovation and progress! I can't find an example now, but there ads from the 1950s essentially extolling the virtues of boxed mac and cheese and how it is essentially science brought into your kitchen to reduce your labor and make you (the homemaker) and your family happy with its salty delicious flavor that can be on the table in a fraction of the preparation time. Food companies that were developing these new products were also trying to create recipes that used them and to popularize those recipes- which still happens today, look on the side of any cream of whatever soup can, they will almost certainly have a recipe included.

Just doing a brief search on McCall's recipe collection whose branding is on that card, every example on the internet seems to include gelatin, or another manufactured food product. It makes you wonder where their recipes came from and who was funding their development...

You can find answers to similar/related questions here (jello, etc. ) collected by /u/Searocksandtrees.

Much of it can be put on two main factors, the Second World War, and the industrialization of food stuffs which occurred from the mid Victorian period, on to the 1950's. These "weird" recipes were usually not something which housewives came up with, but rather things advertisers or sometimes cookery writers invented to use a maximum number of these new processed foods and to be modern, eye catching, colorful, and inventive or exotic. They were also meant to be efficient, and time saving for the modern housewife. This sometimes allowed for work outside the home, for relaxation, for more focus on child-rearing rather than cooking, more focus on keeping the "perfect American home", or more involvement with the community.

Take the ham and bananas in hollandaise. It is a very fast recipe, which requires almost no preparation. It uses bananas, still in the 1950's considered rather exotic. Lemon juice as well would have been seen as a new found luxury to many women of the 1950's. Mustard, gave a mild, familiar flavor. It uses sliced ham, which was economical because it used up leftovers from perhaps a Sunday dinner, or used the same, cheap processed ham bought for lunchtime sandwiches. Lastly, hollandaise, a fancy French sauce associated with upper class dining, and sometimes difficult and time consuming to perfect, especially without a modern kitchen, made simple, accessible, novelty, and modern because it came powdered in a packet. Now think about the colors, particularly the colors you see in the print advertising. The bright yellow of the hollandaise atop the bright pink of the ham would have looked really beautiful to the mid-century eye.

The same can be seen in the prevalence of aspics in mid-century cooking. Aspics were popular since industrially produced powdered and sheet gelatin became available during the Victorian era. Aspic was seen as a normal part of the diet, it was good for preserving food, and were seen as really beautiful. It was a quick way of beautifying a simple meal like a salad, and adding some flavor to rather tasteless canned ingredients. But it was also simply part of how woman had learned to cook in an era before refrigeration. Though most American families in the 1950's had both electricity and refrigeration, this was not necessarily true of the two previous decades when the women cooking for their families in the 1950's would have learned to cook. Savory aspics in particular, were seen as good for the digestion, p'tcha, calf's foot jelly, and kholodets, are all examples of pre-industrial aspics used as a method of preservation. Gelatin salads were popular from the Victorian era on, so trying new, even more processed ingredients such as 7-Up and processed cheese. There isn't really a lot of thought to taste put into recipes like this, which are really more about eye-catching colors for advertisement purposes. It was more meant to get people to buy 7-Up than to make this specific recipe, though I'm sure many people made it.

Some of these recipes were also probably not prepared quite as widely as we think, and were likely seen as fairly novelty to people of the 1950's, though their component processed ingredients would. They were certainly more likely to be found at a dinner party than a nightly dinner.

As you mentioned, the Second World War also had a significant impact on the prevalence of all the processed foods used in these recipes. The US essentially was feeding the world in the late 1940's, as the Western hemisphere was the only land untouched by war, and therefore suitable for agriculture. During the war US food production, agriculture, and food processing boomed to feed Allied soldiers and Allied civilians in the UK and the USSR. In fear of economic depression after the war, many of the factories which made weapons were converted to agricultural supplies, consumer goods, and food processing. This meant a boom in cheap, processed food after the war. There was also an inspirational white middle class, clamoring for new, cheap, modern foods and recipes.

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"Taste of War" Lizzie Collingham

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