Roast pumpkin & spinach lasagne

Name: Roast pumpkin & spinach lasagne
Prep time: 25 min
Cook time: 2 h 5 min
Total time: 2 h 30 min
Cuisine: Italian
Ingredients: 750g Crown Prince pumpkin or butternut squash; 2 tbsp olive oil; 500g spinach washed; 1 tbsp butter plus extra for greasing; whole nutmeg for grating; 6 fresh lasagne sheets; 100g parmesan (or vegetarian alternative), freshly grated; 1 medium onion finely chopped; 1 tbsp olive oil; 1 celery stick, finely chopped; 2 garlic cloves finely chopped; 400g can cherry tomato; 2 tsp light muscovado sugar; 500ml full-fat milk; 6 peppercorns; ½ onion; 1 bay leaf; 50g plain flour; 50g butter