Nonstick cooking spray 1 tablespoon olive, vegetable, or canola oil 1 onion, chopped 1 teaspoon ground cumin 1-1/2 teaspoons chili powder 1 teaspoon minced garlic 1 can (14 ounces) chopped tomatoes, drained, with 1/3 cup juice reserved 1/4 cup tomato paste 2 cans (15.5 ounces each) white, black, or kidney beans (or a mixture of any two), rinsed and drained Kosher or coarse salt and freshly ground black pepper 1 can (15 ounces) sweet corn kernels, drained, or 1-1/2 cups frozen corn, thawed 3 cups coarsely chopped spinach 4 medium-size (8-inch) flour tortillas 2 cups (8 ounces) shredded Monterey Jack or cheddar cheese Chopped fresh cilantro (optional), for garnish Sour cream (optional), for serving Salsa (optional), for serving Preheat the oven to 400°F. Spray a 9-inch round cake pan, springform pan, or baking dish with nonstick cooking spray. Heat the oil in a large skillet over medium heat. Add the onion, cumin, chili powder, and garlic and cook until you can smell the spices and the onion is softened, about 3 minutes. Stir in the tomatoes with the 1/3 cup of reserved juice and the tomato paste, then stir in the beans. Season with salt and pepper to taste. Let the bean mixture simmer until everything is hot, about 3 minutes. Add the corn and spinach and stir until the spinach has wilted and everything is well blended and hot, about 3 minutes. Taste for seasoning, adding more salt and/or pepper as necessary. Place 1 tortilla in the prepared cake pan. Spread one fourth of the bean and vegetable mixture evenly over the tortilla, then sprinkle 1/2 cup of the shredded cheese evenly over the top. Repeat with 3 more layers, ending with the last quarter of the bean mixture and then the last 1/2 cup of shredded cheese. Bake the tortilla casserole until it is hot throughout and the top is lightly browned, about 20 minutes. Let the casserole sit for about 5 minutes, then cut it into wedges using a sharp knife and serve it with a spatula or better yet a pie server. Sprinkle the top with cilantro, if desired, and serve with sour cream and/or salsa on the side, if you like. Cooking Tip: You can make the tortilla casserole a day ahead of time, cover it with plastic wrap or aluminum foil, and put it in the fridge overnight; just take it out and let it sit at room temperature for about 20 minutes while the oven preheats to 400°F. Bake the casserole uncovered. You can also reheat the cooked casserole at 350°F for 15 to 20 minutes, until warm.