Heat the oil and the butter together in a large heavy-based saucepan over a medium heat. Saute the shallots gently for 4-5 minutes then add the garlic and continue to cook for a further 2 minutes.
Add the rice and coat thoroughly in the butter, oil and shallot mixture and cook for 3-4 minutes or until the grains start to turn translucent. Add the white wine and increase the heat to allow it to evaporate almost entirely. Stir in the tomato purée and canned chopped tomatoes, then add a ladle of hot vegetable stock to the risotto, one at a time, stirring frequently until they are absorbed into the rice.
Continue in this fashion until all the stock has been absorbed and the rice is soft yet still defined; usually 30-40 minutes. Adjust the seasoning as necessary then spoon onto serving plates. Garnish with a sprig of oregano leaves before serving.