Melt half the butter in a medium frying pan over medium heat. Add the onion. Reduce heat to low. Cook, stirring occasionally, for 20 minutes or until the onion is soft and slightly caramelised.
Preheat oven to 180°C. Lightly rub a little of the remaining butter over the base and sides of a 2L (8-cup) capacity baking dish. Coarsely chop the remaining butter.
Arrange a layer of potato, slightly overlapping, over the base of the dish. Top with a little of the caramelised onion and a little of the thyme. Continue layering with the remaining potato, caramelised onion and thyme, finishing with a layer of potato. Pour over the stock. Top with the chopped butter. Cover with baking paper and foil. Bake in oven for 1 hour.
Uncover and bake for a further 20 minutes or until the potato is very soft and the top is golden. Set aside for 10 minutes to stand before serving
Serving size: 6
Recipe courtesy of taste.com.au