Kale and Cheddar Melts with Caramelized Onion

This recipe gives basic grilled cheese a tasty—and healthful!—update. We combine earthy wilted kale with sweet caramelized onions and melty cheese, plus a slathering of mustard for tangy contrast. To add a salty-smoky note, tuck crisp bacon slices inside the sandwiches before cooking them. Be sure to use a hearty sandwich bread that’s sturdy enough to contain all of the fillings.