Simple squash risotto

INGREDIENTS

• 1 butternut squash
• 4 tbsp light olive oil
• 600ml vegetable stock
• 50g unsalted butter
• 1 small onion , finely chopped
• 1 celery stick, finely chopped
• 2 garlic cloves , crushed
• 1 bay leaf
• 1 tsp fresh thyme leaves , picked
• 140g risotto rice (we like carnaroli)
• 100ml white wine
• 50g Parmesan (or vegetarian alternative), finely grated