Cortez’ letters to King Carlos are one good source, another is the book written by his officer, Bernal Diaz. When studying in Mexico City, I took a linguistics class and covered some Aztec language (Nahuatl). The people who helped Cortez were of the Tlaxcalla tribe. Not long in the past a prior Aztec governor decided the people needed more protein, so developed the institution of the “flowery” war. The prisoners taken in those wars were sacrificed and eaten. They had no large meat animals like cattle, buffalo, antelope, etc. Only turkeys and chickens and some fish. The Nahuatl word for tortillas is Tlaxcali. Aztecs and other Indians did not die immediately of the flu. Over a century, millions of Indians died of various new diseases. Some estimate the North American Indian population was cut to 1/10th of the number from before the Spaniards showed up.
Cortez wrote they ate the arms and legs of the sacrificed people, and fed the heads and torso to wild pigs.
Bernal D’s “Conquest of New Spain” was one of my texts in a Latin American history class I took. There were a couple of corrections by the translator (Diaz had a couple of small errors involving which village came before the other, that kind of thing) but had first person details otherwise unavailable. The remarkably lucky shot that saved all their remaining asses at Teotihuacan is one of those.
That’s with the usual “if memory serves” proviso.
The Aztecs’ “flower wars” were not limited to just the Tzaxcalla.
And the Aztecs had this long wooden cagelike structure in front of the pyramid of the sun. Their cute name for it was “the corncrib”, but it held the severed heads (and over time, fleshless skulls) of their many human sacrifices.