Eggs, yes? Humans have been eating them for thousands of years. In the West we have some standard ways: fried, scrambled, poached, boiled, hard-boiled, &c. Have these been common for a long time too? How did Europeans in the Middle Ages prepare eggs? Ancient Rome? Bronze Age cultures? I dunno if any professional or amateur historians on reddit are familiar with these minutiae of culinary history, but it would be super fantastic!
An important thing to remember is that even though nearly all eggs eaten today are chicken eggs (with a few exceptions of course), in the past this wasn't necessarily the case. The Ancient Phoenicians and Egyptians make frequent mention of eggs in their myths, but it's usually in reference to ostrich eggs. Similarly, the Chinese seem to be more fond of pigeon eggs in antiquity and the Romans and Indians of the eggs from peafowls. I even remember reading a theory that these or similar forest dwelling fowl from India were among the first birds to be domesticated by humans and it was specifically for their eggs.
As for the preparation of eggs, Most of the methods and styles common now were practiced as far back as antiquity (minus some of the obvious molecular gastronomy things). Boiled eggs were common, espeically in Roman cuisine and were often left or cooked straight in vinegar. The Romans would also often top their boiled eggs with sauces and spices made from anchovies, honey, ground nuts or of course their signature sauce, garum. Really though, throughout history, you'll find that boiled egg recipes are extremely common across many cultures. There's a few reasons for this: it's easy, it only requires four things (eggs, water, a source of heat and a pot) and many houses had to boil water anyways, so you might as well throw a couple of eggs in. Despite the simplicity of this, other methods of cooking eggs were certainly practiced, especially for the true gastronomes.
For example, here's something a little more complex. A recipe for what we might think of as an omelet. This is from the Apicius, a famous collection of Roman recipes compiled in the 4th or 5th centuries AD. Honestly, if you're interested in ancient cuisine, this is a great place to start. It can be found free online too.
Here's a rough translation of the omelet recipe: "Four eggs in half a pint of milk and an ounce of oil well beaten to make a fluffy mixture. In a pan, put a little oil and add the egg preparation without letting it boil. When one side is done, turn it out to a platter. Fold it, pour on honey and sprinkle with spices."
Sources: The Food Lover's Companion (p. 212), Around the Roman Table: Food and Feasting in Ancient Rome (315-3-16), Apicius (http://www.gutenberg.org/files/29728/29728-h/29728-h.htm)