In a strainer lined with cheese cloth or a coffee filter, drain the ricotta for at least 1 hour. In a separate strainer, drain the spinach.
Add the egg and egg yolk to the bowl of an electric mixer and beat for 1 minute.
Add the ricotta and beat for an additional minute.
Squeeze the spinach to get out any extra water then add it, along with the Parmesan, to the bowl. Stir in the salt and pepper as well as the flour and thoroughly mix.
Pour a little flour onto your cooking surface and coat your hands with some extra to help keep the dough from sticking.
Form the ricotta mixture into balls slightly smaller than golf balls.
Dredge each ball in the flour and set aside to rest while you bring a pot of water to a boil.
When the water is boiling, slide the gnudi into the water, being careful not to crowd the pan. You may need to cook in batches. Cook until they all float to the top and have firmed up, about 4 minutes.
Using a slotted spoon, transfer the cooked gnudi to paper towels to drain.
Serve with warm marinara.