Spread a few tablespoons of the marinara sauce in the springform pam. Break one lasagna noodle to make a layer in the pan over the sauce, then dollop an even layer of 1/4 cup of the ricotta mixture in tiny bits on top, followed by a sprinkled, even layer of 1/4 cup mozzarella. Make three more layers, using 1/3 cup marinara sauce, a broken lasagna noodle, 1/4 cup ricotta mixture, and 1/4 cup mozzarella for each. After each layer, press the noodle bits down slightly to help spread out the ricotta below. Finish up with half of the remaining marinara sauce, the last lasagna noodle, the remainder of the marinara sauce, and the Parmigiano-Reggiano in an even layer. Cover the springform pan tightly with aluminum foil. Use the sling to lower the pan onto the trivet in the pot; fold down the ends of the sling so they fit inside the pot. Lock the lid on the cooker.