Steps
- Preheat the oven to 350°F / 180°C. Grease a 9in / 23cm square baking dish with a little of 25g of butter.
- Put the grated zest of 1 large lemon, leaves of 4 thyme sprigs, and ½ teaspoon of grated nutmeg in a large saucepan.
- Add 200ml of heavy cream and 200ml of vegetable broth, season, and bring to a simmer. Stir in 1.25kg of peeled very thinly sliced potatoes and cook gently for 8 minutes, stirring occasionally.
- Transfer the potatoes and liquid to the dish and dot with the remaining butter. Cover with foil and bake for 30 minutes.
- Uncover and bake for 30-40 minutes, until tender and golden. Let cool for 15 minutes.