Winter Greens and Potato Casserole

INGREDIENTS

8 cups

water

12 cups

chopped kale, stems removed (about 1/2 pound)

12 cups

chopped mustard greens, stems removed (about 1/2 pound)

6 cups

(1/8-inch-thick) slices red potatoes (about 2 pounds), divided

Cooking spray

2 cups

vertically sliced onion, divided

3/4 tsp

salt, divided

1 cup

shredded sharp provolone cheese, divided

1/2 cup

canned vegetable broth