Turn the pot to SAUTE. Add olive oil to the pot, then and the spinach. Saute until it wilts all the way down. Season with salt and pepper to taste. Then pour the spinach into a strainer to remove any extra liquid. Set aside.
In a bowl, make the filling by mixing ricotta, 1 cup mozzarella, parmesan, garlic, egg, salt, pepper, and spinach. Use a spoon to scoop into the uncooked shells.
Once all shells are filled, spray the liner of the Instant Pot with nonstick spray. Add the broth into the pot. Then add the stuffed shells, stacking on top of one another if necessary.
Pour the marinara marinara sauce over all of the shells. If you need more marinara sauce to cover the shells completely, you can use more. Any shells not covered by liquid will not cook correctly and will come out hard.
Put the lid on the Instant Pot and set the pressure to HIGH for 9 minutes. Perform Quick Release immediately after the timer goes off.
Open the lid and sprinkle the remaining 1 cup of mozzarella cheese on top of the shells. Put the lid back on (don’t turn the pot on) and allow the residual heat to melt the cheese for about 3 minutes. Open the lid and serve. Enjoy!