"Wilt" tender greens; braise heartier ones
I used to get home and wonder what in the world I was going to do with all those greens, but not any more. Working away in my warm kitchen on chilly days, I've developed a little repertoire of recipes (side dishes, soups, and light suppers) for cooking these cool-weather greens. In the process, I've discovered that greens have different personalities. Some—like beet greens, Swiss chard, and spinach—are so tender that they need only a touch of heat to be cooked. Overcooking them, in fact, tends to alter their flavors in an unpleasant way. While these greens are best "wilted," the heartier greens, like kale, mustard, collards, and turnip greens, will be tough and leathery unless patiently simmered. The assertive flavors of these greens also mellow with cooking and blend with the aromatics with which they're cooked.
There are a few cooking greens that can be wilted or braised. You might think of escarole or dandelion greens as hearty lettuces best suited for warm salads, but both of these greens (especially older, larger leaves) are delicious braised or added to soups, though cooking them too long, unlike the very hearty greens, will not improve their flavor.