Bring the stock to a simmer in a pan on a low heat. Peel the onion, trim the celery, then finely chop or coarsely grate them. Put 1 tablespoon of olive oil, 1 knob of butter, plus the onion and celery into a high-sided pan on a low heat. Season lightly with sea salt and black pepper and cook for 5 to 10 minutes, stirring occasionally, until the veg is soft but not coloured. Turn up the heat to medium, add the rice and stir for 2 minutes, so it sucks up all the lovely flavour. If using, pour in the wine and stir until absorbed. Add a ladleful of hot stock, stir, and wait until it’s been fully absorbed before adding more. Cook for 16 to 18 minutes, adding more stock every minute or so and stirring regularly, until the rice is al dente. This means it should be soft and a pleasure to eat, but still holding its shape. About 5 minutes before your rice is ready, stir in the frozen veg to cook through. Now, your risotto needs to be slightly looser than you want it to be, as it will thicken as it sits, so add an extra ladleful of stock. Turn off the heat, stir or beat in the remaining butter and the Parmesan, then season to perfection. Pop the lid on and let it sit for 2 minutes before serving. The most important thing is that the risotto is always oozy. Finish with a drizzle of extra virgin olive oil, an extra grating of cheese and, if you’ve got it, a tiny squeeze of lemon juice per portion.