Butternut squash soup with chilli & crème fraîche

INGREDIENTS

• 1 butternut squash , about 1kg, peeled and deseeded
• 2 tbsp olive oil
• 1 tbsp butter
• 2 onions , diced
• 1 garlic clove , thinly sliced
• 2 mild red chillies , deseeded and finely chopped
• 850ml hot vegetable stock
• 4 tbsp crème fraîche , plus more to serve