ounces of the best, thickest center-cut bacon you can find
large cloves garlic, crushed
cup chicken or vegetable stock (for long-cooking greens only)
Tablespoons apple cider vinegar
ounces feta cheese
Salt and pepper
Wash the greens in several changes of water and dry thoroughly. Strip the greens from their stems and tear into large bite-size pieces. If the stems are tender (yes for beets, chard, dandelion, mustard / no for kale and collards), chop them into 1-inch segments.
Start with a skillet that is wide enough to embarrass you at the thought of using it to cook lunch for one. Heat it on the stovetop over medium-high heat. Chop the bacon into 1-inch pieces and add to the heated skillet. Cook, stirring occasionally, until the bacon is about 2/3 as crisp as you would like it and has given off plenty of fat.
If you will be cooking your stems, add them to the skillet now, along with the garlic. If not, just add the garlic. Cook, stirring occasionally, for two minutes.
Add the greens to the skillet and stir (preferably with tongs) to coat all the greens with a bit of bacon fat. For relatively tender greens (all but collards and kale): Cook uncovered until the greens are just shy of desired tenderness. Add the cider vinegar and cook for one minute more. For collards and kale: Cook uncovered for a few minutes, then add the stock or water and cider vinegar. Cover, lower the heat to maintain a simmer, and cook to desired tenderness, probably about 10 minutes. Season with salt and pepper.
Place the greens in a bowl, crumble the feta cheese overtop, and serve.