Stir fry the onion with butter until softened, add the peeled and crumbled sausage and the hearts of artichokes, thinly sliced. Cook for five minutes then add the tomato puree and let it simmer for another five minutes.
Meanwhile cook the rice in boiling water for 3 minutes, drain and add it to the pan with artichokes, sausage and tomato sauce. Add also the grated Parmigiano and stir to mix all the ingredients. Season with salt to taste.
Preheat oven to 200°C and Spread the rice in a ceramic baking dish. It should be at least 5 cm thick. Level the surface, sprinkle some fresh thyme on top and drizzle with extra virgin olive oil. Bake for about 35-40 minutes, until the rice is dry and covered with a golden crust.