Cooking greens are mature or "tougher greens" like swiss chard, collards, kale, spinach, beet greens, turnip greens, mustard greens, dandelion greens etc. Delicious as a side dish, or added to soups (like minestrone).
Any greens (as described above)
Bacon drippings (or other fat such as butter, coconut oil, olive oil)
Heat bacon drippings in a cast-iron skillet over medium heat. Add the greens. Stir-fry, you are stirring and frying, for 1 to 4 minutes (depends on how tough the greens are) or until greens are limp, tender, bright green, and have greatly reduced in size. Bacon fat is good because it helps bring out their great flavor. (Non-meat-eaters use coconut oil, olive oil, or butter)
Step 2 (Optional)
At this point, you have a choice. Either serve them straight from the pan with a sprinkling of salt, or add 3 to 4 cups of water and salt to taste, and boil the greens or add to a soup (1 hour for extra tender, probably-won't-even-have-to-chew greens).
(This is an East Coast or “Newfie Greens”, boiled dinner favourite)