Heat oil in a frying pan over medium low heat. Add vermicelli and fry for 2-3 minutes until golden. Drain the vermicelli and set aside; reserve oil. Place onion, garlic, salt and tomatoes in a blender or food processor and process until smooth. Heat reserved oil in the frying pan over medium heat, then pour in tomato mixture. Cook for 5 minutes, stirring constantly.
put vermicelli tomato mixture and stock into a large saucepan. Season with salt and pepper. Cover and bring slowly to the boil, then simmer for 10 minutes until vermicelli is tender. stir in sherry. Pour into a warmed tureen. Garnish with chopped coriander. Serve with grated Parmesan cheese.