Preheat the pan with 30g butter. Add the onion and stir until golden brown. Add spinach, wait 3 minutes and set aside.
Preheat the oven to 150 degrees.
In the large bowl mix together: ricotta, 40g parmesan, eggs and egg yolk, salt, nutmeg, pepper and spinach. When all ingredients are well-combined add flour, mix everything well and correct seasoning.
Prepare a large pot with salty, boiling water. Form the gnocchi with 2 wet teaspoons from the prepared mixture. Cook them on low heat for 5 minutes, until they come out from the water.
Melt the rest of the butter in the pan. Take out the gnocchi, trickle them with some butter and rest of the parmesan.
Bake gnocchi for about 5 minutes.