Preheat the oven to 200C mark 6.
Halve or quarter the tomatoes, depending on their size, drizzles with 2 tbsp olive oil and season well and roast for 30 minutes. Leave to cool for a few minutes and then blitz with a stick blender or crush with a fork.
Heat 2 tbsp of oil in a large, ovenproof casserole dish (that has a lid). Add the onion and garlic and cook gently for five minutes. Add the rice, and cook, stirring, for 1 minute.
Pour in the tomato mixture and stock, season and bring to a simmer, stirring. Cover with a lid and cook in the oven for 20 minutes.
Meanwhile, put the cherry/plum tomatoes on a small baking tray, drizzle with remaining oil and season. Cook in the oven for 15 minutes until starting to split and soften.
Remove risotto from oven, stir in most of the parmesan and all the mozzarella. Re-cover with the lid and return to oven for 10 minutes, until the rice is tender, and the liquid has been absorbed.
Sprinkle over remaining Parmesan and top with the roasted cherry tomatoes to serve.
