Bring a large pot of salted water to a boil. Add greens to pot and cook for 7 minutes or until tender. Using a slotted spoon, place in a cold water bath, then drain well and squeeze out any excess water; chop finely and set aside.
Bring another large pot of salted water to a boil.
Place 1 cup of the flour in a shallow pie plate.
In a large bowl, stir together chopped greens, 3/4 cup remaining flour, Parmesan, yogurt, ricotta, eggs, egg yolk, salt and pepper. Drop mixture by the heaping tablespoonful into pie plate; gently roll to coat with flour, then toss between hands to tap off any excess
Carefully slide gnudi into boiling water, working in batches so as to not overcrowd the pot. Once gnudi have floated to the top, allow to cook for another 2 minutes. Remove using a slotted spoon and serve with marinara sauce.