Jemma O'Hanlon's Foodwatch - Super-quick spinach soup

Ingredients

• 1-2 tablespoons olive oil
• 1 onion, finely chopped
• 2 tablespoon plain (all purpose) flour
• 2 cups chicken or vegetable stock, reduced-salt
• ½ cup milk
• 250 g pack frozen chopped spinach
• pinch of nutmeg
• TO SERVE:
• Thick Greek yoghurt