Blend tomatoes.
Heat blended tomatoes, water and stock in a saucepan. Bring to a gentle simmer and keep over a low heat.
Melt the butter and oil a large pan. Add the onion and gently cook until softened.
Stir in the garlic and rosemary, then cook for 1 min more.
Add the rice and cook, stirring, for 1 min.
Start adding the hot stock and tomato mixture about a cup at a time. Let the risotto cook, stirring often, adding more stock as it is absorbed.
After you have added half the stock, add the cherry tomatoes.
When the rice is creamy and tender, the cherry tomatoes softened, cover and leave for 1 min, then stir in the basil and parmesan.
Serve sprinkled with Parmesan and a good grinding of black pepper.