Add 2 cups water to a 6-quart Instant Pot® and set the rack inside with the handles folded under.
Mix together the ricotta, mozzarella, Parmesan, parsley, egg, 1 teaspoon salt and a few grinds of pepper in a medium bowl to combine.
Spread 1/2 cup marinara in the bottom of an 8-inch round cake pan. Break 4 lasagna noodles into large pieces and arrange in an even layer over the marinara. Spread another 1/2 cup marinara evenly over the noodles followed by a third of the ricotta mixture spread in an even layer. Top with another layer of 4 broken lasagna noodles. Repeat the process 2 more times, for 2 more layers of marinara, noodles, marinara, ricotta, noodles. Top with the remaining marinara and cover tightly with foil, making sure to wrap any excess underneath the pan so that it will fit in the pot.
Fold an 18-inch piece of foil in half lengthwise, then fold it in half again lengthwise and finally once more in half lengthwise making a 4 1/2-inch-wide foil sling for the pan. Place the lasagna pan in the center of the sling and, lifting the two ends of the sling, lower the pan into the pot.
Follow the manufacturer's guide for locking the lid and preparing to cook. Set to pressure cook on high pressure for 25 minutes (see Cook's Note). After the pressure cook cycle is complete, follow the manufacturer's guide for natural release. After 15 minutes, being careful of any remaining steam, unlock and remove the lid.
Remove the lasagna from the pot and let rest 10 minutes. Carefully remove the foil (steam will be locked inside) and serve.
Settings may vary on your Instant Pot® depending on the model. Please refer to the manufacturer's guide.
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