Heat oven to 200C/fan 180C/gas 6. Heat the oil and butter in a large roasting tin. Add the garlic and cook over a medium heat for 2 mins. Tip in the potatoes and toss to coat in the garlic butter and oil.
Pour the stock over the potatoes and season with pepper and a little salt. Bring to the boil then transfer to the oven. Cook for 40-45 mins or until tender.
Transfer to the stove-top and toss over a medium heat until most of the liquid has been absorbed and turned to a shiny glaze – about 15 mins. Tip potatoes into a warm serving dish and scatter over the thyme and serve.