BBC Food - Recipes - Spring minestrone soup with pesto

Ingredients

• 3 tbsp olive oil
• 40g/1½oz butter
• 2 large onions , finely chopped
• 1 leek , halved lengthways and thinly sliced
• 250g/9oz potatoes, peeled and finely chopped
• 3 sticks celery , finely chopped
• 150g/5oz savoy cabbage
• 2 litres/3½ pints beef or vegetable stock
• 400g/14oz can Italian chopped tomatoes
• salt and freshly ground black pepper
• 2 tbsp green basil pesto