I learned this easy way of cooking greens in the cookbook Artichokes to Za'atar. It's worked nicely with all sorts of greens, from beet to collared. More tender greens take less time to cook. Beet greens have taken about 10 minutes; collareds about 20.
any sort of onion, diced
1 bunch greens, washed, trimmed, and roughly chopped
1 clove garlic, smashed with 1/2 teaspoon salt
juice of 1 lemon, or the same amount of water plus a little preserved lemon brine
1 teaspoon pesto; 1/4 of a preserved lemon, minced; or other condiment
In a pan or pot large enough to hold the raw greens, fry the onions in the oil until soft, about 2 minutes. Add the greens and garlic and cook until wilted. Add the lemon juice. Cover, lower heat, and cook for 10-20 minutes, until greens are soft. Remove the lid, turn up the heat, and stir in the pesto. Serve.
It's nice when there's some broth, and it's also good when all the broth has cooked away.
Beet greens produce a gorgeous fuscia broth.