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.