Heat the oil over a medium heat in a large casserole dish. Add the onions and cook for 3 to 5 minutes, until softened, then add the garlic and cook for 2 minutes. Push the onions and garlic to the edge of the pan, add the chicken breasts and cook for 3 to 4 minutes on each side to brown. Sprinkle over the flour and stir it into the onion mixture. Add the stock and season. Cover and simmer for 10 minutes – or until the chicken is cooked through. Using 2 forks, shred the chicken into bite-sized chunks. Add half the mascarpone and the pesto, stirring until the mascarpone has melted into the sauce, bubble for 2 to 3 minutes to thicken a little, then remove from the heat and stir in the basil.

Heat oven to 180C/160C fan/gas 4. Meanwhile, place the squash in a large bowl with 2 tbsp of water, cover with cling film and microwave on high for 12 to 15 minutes, until really soft. Season the squash with a little of the nutmeg and some salt and pepper, and mash lightly with a fork.

Spoon half the chicken mixture into the bottom of a 20 x 30cm ovenproof dish. Cover with 4 lasagne sheets, then the butternut squash and half the Parmesan. Top with another 4 lasagne sheets, the remaining chicken mixture, then a final layer of lasagne. Mix enough milk into the remaining mascarpone to make a smooth sauce – you need to aim for a consistency similar to a white sauce. Season with the remaining nutmeg and some salt and pepper, then pour over the lasagne. Scatter over the remaining parmesan and the pine nuts. Bake for 40 minutes until piping hot in the centre and crunchy and golden on top. Scatter with a few extra basil leaves before serving.