Kale, curly or flat (aka Tuscan, lacinato or dinosaur), or spinach
Olive or other kind of oil (lightly garlic-infused oil if you're fancy)
Smoked paprika or other spices, if you're really fancy, optional
Preheat your oven to 275 degrees.
If using kale, hold the thick stem between two fingers and strip the leaf from the stem; if the stem is thick through the middle of the leaf, it's better to strip it so the leaf comes apart in two pieces. If using spinach, do the same if the stem is thick. Baby spinach leaves are fine as they are.
Toss the leaves with a splash of oil, enough to lightly coat, not drown them. If you're using kale, give the leaves a nice rub with your fingers to get the oil all over them. Season lightly with salt (as the leaves dehydrate, they'll shrink, so the chips will taste much saltier than when they go in).
Lay leaves flat on a baking sheet; don't overlap them, but they can be close to one another. Bake until they're dried, crisp and crackly with no chewiness left, about 26 minutes for curly kale, 24 for flat kale, 18 for spinach or 15 for baby spinach leaves. In any event, be sure not to bake them for too long, lest they brown and get too intense.
Once they're done, you can lightly sprinkle them with spices. Store in an airtight container.
Francis Lam is Features Editor at Gilt Taste, provides color commentary for the Cooking Channel show Food(ography), and tweets at @francis_lam.