Spring minestrone

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

1. Heat the oil and butter in a large pan. Add onions, leek and potatoes and cook for about five minutes, until starting to soften, stirring from time to time. Add the celery and cook for a few minutes more.
2. Meanwhile cut the half cabbage in quarters. Remove central stalk from cabbage and discard. Cut leaves across the wedge shape in short shreds.
3. Pour stock and can of tomatoes into the pan with the cabbage. Bring to the boil.
4. Season with salt and pepper and gently simmer for about 30 mins.
5. Add pesto for the last 5 mins, and check the seasoning before serving.