Heat your oven to 180C/350F.
- Heat your oil in a large saute pan over a medium heat. Add your onion, celery, carrot and pepper and saute for 5 mins, until soft. Add your passatta, salt and pepper and bring to a simmer. Put a lid on a pan and simmer for 15 mins, until rich and thick.
- Combine your spinach, mozzarella, parmesan, ricotta, cream cheese, sour cream, garlic, nutmeg, salt and pepper in a bowl and stir to combine.
- Grease a large heatproof bowl with butter and line with greaseproof paper. Grease this with butter, then arrange your lasagne sheets around the edge in a spiral, ensuring there is some hanging over the edge.
- Sprinkle with a little mozzarella, then about half of the spinach and ricotta mix. Smooth it down, then top with some lasagna sheets (cut them in half if necessary to slot them in). Add a little more mozzarella, then top with three quarters of the tomato sauce. Lay more lasagna sheets over the top and add the rest of your spinach and ricotta mix.
- Pull your overhanging lasagna sheets into the centre to seal in the filling. Bake in the oven for 45 mins.
- Blitz your remaining tomato sauce until smooth. Once your lasagne is out the oven, gently turn the bowl out onto a lined baking tray. Pour your tomato sauce over the centre, then sprinkle with your remaining mozzarella.
- Place under a medium grill for about 5 mins, until the cheese is golden and bubbly.
- Sprinkle with basil and serve!