In a large bowl, combine ricotta cheese, Parmigiano Reggiano, spinach, a large egg, and ¾ cup of all-purpose flour. Season with a generous pinch of salt and mix until well combined.
Scoop the ricotta mixture into 1-tablespoon-sized balls and roll them in flour. Let them rest, uncovered, in the fridge for 1 hour.
When ready to cook, bring a large pot of salted water to a boil, then reduce the heat to maintain a light simmer. Working in batches, gently lower a few gnudi into the water and cook for 2–3 minutes, or until they float to the surface.
In a separate pan, melt the butter and add in the lemon juice. Add the strained gnudi and cook for 1 minute. Top with fresh herbs and serve.
