Preheat the oven to 160ºC/325ºF/gas 3. Peel and finely chop the onions, celery and 2 cloves of garlic. Cut the green part off the leeks (save for making stock or soup), then trim, wash and finely chop the white part. Peel the potatoes and chop into ½cm dice. Tie the thyme sprigs together. Melt half the butter in a large pan on a low heat with 1 tablespoon of oil, then add the onions, garlic, celery, leeks, potatoes, bay leaves and thyme. Cover and sweat down for 15 minutes, or until softened, stirring occasionally. Add all the mince to the pan, breaking it up with a wooden spoon. Turn the heat up to medium-high and cook for 10 more minutes, or until the mince is browned all over, stirring occasionally. Pour in the wine, let it bubble and boil away, then finely grate in half the nutmeg. Stir in the flour for 1 minute, then pour in the milk. Season with sea salt and black pepper, cover with a scrunched-up sheet of wet greaseproof paper and transfer to the oven for 2 hours, or until thickened and beautifully tender. At this stage, the ragù might look like it’s split a little, but this is actually what we’re looking for – the milk in the sauce creates amazing ricotta-like curds as it cooks. Meanwhile, place a large heatproof baking dish on a medium heat with 2 tablespoons of oil and the remaining butter. Peel, finely chop and add the remaining garlic, along with the chilli flakes, nettles (leaves only – wear gloves to protect your hands while you prep) and spinach – you’ll need to work in batches. Cook for 10 minutes, or until softened. Allow to cool, then finely chop and return to the dish, spreading evenly over the base. Once done, divide the ragù in two, freezing one half for another day, once cool. Carefully drain the liquid from the remaining ragù into a bowl through a coarse sieve. Return the ragù to the pan, fish out and discard the thyme stalks and bay, then grate in half the cheese and stir well. Turn the oven up to 180ºC/350ºF/gas 4. Use a piping bag or teaspoon to stuff the cannelloni tubes with the ragù, then arrange on top of the greens. Pour the sieved liquid over the top and grate over the remaining cheese. Trim and finely slice the mushrooms and scatter over the cannelloni. Drizzle with 1 tablespoon of oil, then bake for 40 to 45 minutes, or until golden and bubbling. For added colour, flash the dish under the grill for 5 minutes. Importantly, let it stand for 30 minutes before serving. Delicious with a seasonal salad for added crunch.