Preheat oven to 200C/400F/Gas 6.
Drizzle two teaspoons of the olive oil over the butternut squash and place onto a baking sheet. Place into the oven and roast for 10-15 minutes, until tender.
Heat the remaining teaspoon of oil in a saucepan over a high heat. Add the garlic and fry for one minute.
Add the potato and fry for two minutes.
Add the stock and spinach leaves and simmer for 2-3 minutes, or until the spinach has wilted. Transfer the soup to a food processor and blend until smooth.
To serve, divide the roasted butternut squash between two bowls and pour over the soup. Garnish with the yoghurt.