You can make this vegan by leaving out the butter.
Heat the butter and the olive oil in a large pot and add the onion. Cook, stirring, until the onion is soft and translucent, and then add the cabbage. Season with salt and pepper, and cook, stirring, over a medium heat for 5 minutes. Turn down the heat, stir in the walnuts and continue cooking for about 10 more minutes. Add the stock and cook, stirring often, for 15 minutes more or until the liquid is completely absorbed. Check seasoning and serve.
1 Savoy cabbage, leaves rinsed and roughly chopped
2 medium onions, peeled and finely sliced
50g unsalted butter
2 tbs extra-virgin olive oil
60g walnuts, chopped
200ml vegetable stock
Salt and pepper to taste