This is my new favorite way to cook spinach. It's very simple, but really good.
Finely dice one large clove of garlic. Set a cast iron pan on medium heat and add a knob of butter. Sautee the garlic until quietly fragrant, add a pinch of chili flakes, then a fistful of spinach. Salt and pepper. Toss the spinach to coat with butter, and cook until wilted. Then add some more spinach--you'll be surprised how much spinach you can cook in this manner. Continue to add salt & pepper in small amounts as you add more greens to the pan. Taste for seasoning and serve.