1. Preheat the oven to 180°C, fan 160°C, gas 4. Put the potatoes in a large pan, cover with cold water and boil for 15 minutes, until tender. Drain. Meanwhile, in another pan, boil the cabbage and leeks for 5 minutes. Drain, add to the potatoes and mash together with the butter and milk. Season with freshly ground black pepper. Set aside.