Heat 20 g/¾ oz/1 generous tablespoon of butter and the olive oil in a large, heavy-based saucepan set over a medium heat. Add the onion and a couple of the basil leaves and sweat for 2 minutes.

Stir in the tomatoes and continue to sweat for 1 minute. Stir in the rice, making sure each grain is coated in oil. Add the wine and cook until the rice has absorbed it.

Then add a couple of ladles of hot stock, stirring with a wooden spoon until the rice has absorbed it all. Add a couple more ladles of stock and continue to cook in this way, stirring and adding more stock, for 17–20 minutes, until the risotto is cooked al dente.

Remove from the heat and add the remaining butter and mozzarella, stirring well until it has nicely melted into the risotto.

Stir in the grated Parmesan and remaining basil leaves and serve immediately.