Roast pumpkin & spinach lasagne

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 tomatoes
• 2 tsp light muscovado sugar
• 500ml full-fat milk
• 6 peppercorns
• ½ onion
• 1 bay leaf
• 50g plain flour
• 50g butter