For the longest time I assumed that it was Amon’s dawning realization that he was eating his friends all along, but I did a little research considering that I’ve never actually had zenzai. Taking from this article here (x):
Zenzai is a traditional Japanese dessert. It’s a thick sweet soup that consists of boiled azuki beans and is often served with mochi (rice cake) or shiratama dango (glutinous rice flour dumplings )
So basically the ingredients consist of red bean paste or mochi/rice dumplings filled with coconut. Aka there’s no meat because that would be like putting putting chunks of beef in your hot chocolate
So why did Amon randomly think of the soup incident at Donato’s goriest moment? Simple: it’s because he was reflecting on a time when Donato was acting truly as family to him, hence the juxtaposition between Donato ending their little family:
And when Donato was acting as a real father would
Now that’s not to say that I still don’t headcanon Donato feeding Amon and possibly the other children human remains because:
My brother’s gf made these. The dark red thing is azuki beans. The green dango is green tea. And the yellow powder is soy powder. She made the dumplings with glutinous rice flour and tofu so they’re healthy.