For folks not used to growing & cooking greens, maybe a short lesson here. Here is a collard plant. I love collards because they are so easy to grow & one plant produces so many large leaves. You pick the lower, large leaves & small new leaves keep growing from the top. Being large leaves, they are exceptionally easy to clean & process... as opposed to say turnip greens. What I show below will work with amaranth leaves just as well.
Note here the large leaves have been picked. In a week or so, these plants will be ready to pick again.
For reference, here is Lacinato kale. I treat it interchangeably with collards. Grows similarly but the leaves are slimmer & longer. Collards can handle warm weather better than kale.
Processing the collard leaves. After washing the leaves & removing the center stem, I roll a stack of leaves like a cigar and then slice in strips of about 1/2". If you want small pieces, just chop again. I generally just do the single cut. With an average leaf being 8' - 10' wide, with the center stem removed, the cut pieces end up being around 4" long. Since the greens shrink some during cooking, this works fine for me. At this point, they are ready to go in the pot.
Here is a pot of collard, white bean & Italian sausage soup. Now when I just cook the greens as a side dish, I start with some chopped onion & peppers, sauteed in a bit of oil. I then add chicken stock, smoked ham hocks and/or bacon and the leaves. Not unusual to added some red pepper flakes, a bit of sugar and some vinegar. Once it comes to a boil, reduce the heat & simmer for at least 2 hours.