In a pot, bring salted water to a boil, and add the Arborio rice. Stir constantly for the first minute to prevent the rice from sticking to the pot. In a separate pot, add the spinach along with 1/4 cup of water, and cook for a few minutes. Once the spinach has softened, remove it from the heat, and puree using a food processor. Cook the rice for approximately 12 minutes, or before the rice gets to the al dente stage. Pour most of the water out of the pot, leaving 1/4 of the water behind with the rice. Add the pureed spinach to the rice, and cook a few minutes more on low heat. Add the soft ricotta, grated cheese and butter into the rice, and stir until it is uniform and creamy. Salt to taste. Transfer the rice to a warm plate and drizzle with extra-virgin olive oil. Serve immediately.