Preheat oven to 200°C (400°F). To make the sumac salt, combine the salt, sumac and chilli flakes and set aside.
Place the stock, sage, thyme, oregano and garlic in a deep saucepan over high heat and bring to the boil. Add the cauliflower, reduce the heat to low, cover and simmer for 8–10 minutes or until tender. Remove the cauliflower from the saucepan and strain the stock. Reserve the herbs and garlic and transfer to a baking tray lined with non-stick baking paper. Top with the cauliflower, spoon over the combined butter and oil and bake for 30–35 minutes or until golden. Serve the cauliflower with the sumac salt.