A ho-hum sheet-pan of potatoes and greens this is not. Caramelizing sweet potatoes and wilting soft greens on a sheet pan is a smart way to cook two vegetables at once in this efficient and exciting recipe. There are bolts of pickled jalapeño, salty feta and scallions, but the pickled jalapeño brine is the key. It’s used like a spicy vinegar, seeping into the sweet potatoes to complement their flavor. To make it a meal, top with a fried egg or roasted Mexican chorizo, swaddle in a pita or tortilla with tahini or sour cream, spoon onto grains or brothy beans, or into omelets or frittatas. Leftovers will keep refrigerated for up to a week.