Place pumpkin, onion, apple and garlic into a large roasting pan. Drizzle with olive oil, sprinkle over cinnamon, sea salt and freshly ground black pepper and grate over nutmeg. Toss vegetables to coat.
Bake vegetables in oven for about 30 minutes or until cooked and softened.
Remove tray from oven and set aside to cool slightly. Once cool enough to handle, remove skin from pumpkin and squeeze garlic from its skin, then transfer vegetables to a large saucepan.
Add stock to pan and bring to the boil. Reduce heat to a gentle simmer and cook for a further 15 minutes or until vegetables are tender.
Remove pan from heat, then using a stick blender, puree until smooth, adding more stock if necessary. Season to taste. Alternatively, you can use a blender. For a very smooth soup, strain mixture through a fine sieve.
To serve, heat olive oil in a frying pan over medium-high heat. Add sage leaves and cook until crispy, then remove from pan and drain on paper towel. Add bacon and cook until light golden, then add pepitas, and cook for a further minute. Add sugar and stir until melted and caramel is sticking to bacon and pepitas.
Divide soup among bowls. Sprinkle with pepita mixture and crispy sage leaves. Season to taste.