Cook the Chicken: Heat olive oil in a large casserole dish. Add onions and cook until softened. Add garlic and cook for 2-3 minutes. Push the onions and garlic to the side, add chicken breasts, and brown for a few minutes on each side. Sprinkle flour over the mixture, stir to combine, and add chicken stock. Simmer for 10 minutes until the chicken is cooked. Shred the chicken into bite-sized pieces.

Prepare the Sauce: Stir half of the mascarpone and pesto into the chicken mixture, allowing the mascarpone to melt into the sauce. Let it bubble for a few minutes to thicken, then remove from the heat. Stir in chopped basil.

Prepare the Squash: In a large bowl, microwave squash chunks with 2 tbsp water, covered, on high for 12-15 minutes until soft. Season with salt, pepper, and a pinch of nutmeg. Mash lightly with a fork.

Assemble the Lasagne: Preheat oven to 180°C (160°C fan) or gas mark 4. Spoon half of the chicken mixture into the bottom of a 20 x 30 cm ovenproof dish. Cover with 4 lasagne sheets, then spread the mashed squash on top, followed by half of the grated Parmesan. Top with another 4 lasagne sheets, then the remaining chicken mixture. Add the final layer of lasagne sheets.

Make the White Sauce: Mix the remaining mascarpone with a splash of milk to create a smooth, white sauce consistency. Season with remaining nutmeg, salt, and pepper. Pour this over the lasagne. Sprinkle with the remaining Parmesan and pine nuts.

Bake: Bake for 40 minutes, until piping hot in the center and golden brown on top. Garnish with fresh basil leaves before serving.