– 2 tablespoons olive oil – 1 medium onion, finely chopped – 1 large leek, trimmed and halved, white parts thinly sliced – 1/2 teaspoon sea salt, plus more to taste – 1 teaspoon dried thyme, plus more to taste – 12 oz (350 g) Brussels sprouts, ends trimmed, yellow leaves removed, sliced into small disk – 12 oz (350 g) broccoli florets, from 1 medium-to-large broccoli – 27 oz (750 g) cauliflower florets, from 1 large cauliflower – 5 1/2 cups (1300 ml) vegetable stock – 1 small bunch parsley, roughly chopped – 1 1/3 cups (150 g) raw cashew – black pepper, to taste Serve with (optional) – sour cream or creme fraiche, or a vegan alternative – cashews, roughly chopped – fresh herbs, such as parsley and chive