Cook the broad beans in a saucepan of boiling water for 1 minute. Refresh under cold running water. Drain. Peel off the skins and discard. Set aside.
Put the stock in a large saucepan and bring to the boil over high heat. Reduce the heat to low and keep the stock at a simmer.
Heat the oil in a large heavy-based saucepan over medium heat. Add the leek and cook, stirring, for 5 minutes or until soft. Add the garlic and thyme leaves and cook, stirring, for 1 minute or until fragrant. Add the rice and white quinoa and stir for 1–2 minutes or until the grains are well coated in the oil. Add the wine and simmer until reduced by half.
Gradually add the simmering stock, a cup at a time, stirring constantly and making sure the stock is absorbed before you add more. This will take 15–20 minutes; the rice should be al dente yet creamy.
Stir in the peas and broad beans. Simmer for 2–3 minutes or until the vegetables are just tender, then remove from the heat and stir in the parmesan and lemon zest. Cover and set aside for 3 minutes. Season to taste with sea salt and freshly ground black pepper. Serve garnished with mint, with extra parmesan.