Mary Berry’s puy lentil and pearl barley soup

Ingredients

• 1 tbsp olive oil
• 1 large onion, finely chopped
• 2 carrots, finely diced
• 2 garlic cloves, crushed
• 100g (3½ oz) dried Puy lentils
• 100g (3½ oz) pearl barley
• 680g jar passata
• 1.5 litres (2¼ pints) chicken stock or vegetable stock
• Salt and freshly ground black pepper
• 2 tsp sugar
• 1 tbsp balsamic vinegar