Leek and ham hock gratin with rösti topping

Method

1. Melt 50g of the butter in a large sauté pan and add the leeks. Cook over a medium heat for 5-6 minutes, turning occasionally, until the leeks are lightly browned and golden all over. Remove the leeks, leaving the butter in the pan. Heat the oven to 200°C/fan180°C/gas 6.
2. Add the garlic to the butter and cook gently for a few minutes until fragrant. Grate in the nutmeg, then stir through the flour. Increase the heat to medium and cook, stirring, for 2-3 minutes – the mixture should be thick and paste-like. Gradually, in a thin stream, pour in the chicken stock, stirring constantly – the mixture should thicken quickly, then gradually thin out, but always stay thick enough to coat the back of a spoon. If it becomes too thin, stop adding liquid and let it bubble for a minute. Once you’ve added all the stock, pour in the milk in the same way, but a little more quickly. You should end up with a glossy sauce with the consistency of double cream. Add the bay leaves and bubble for 2-3 minutes.
3. Put the leeks in a 1.5 litre ovenproof gratin dish and scatter with the ham. Pour over the sauce and top with the parmesan. Give it a gentle stir, then taste and season.
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4. Melt the remaining butter in a pan and set aside (see know-how). Peel the potatoes, grate coarsely, then put in the centre of a double layer of muslin or clean J-Cloth. Gather the cloth around and squeeze firmly to remove any excess water.
5. Tip the potatoes into a bowl, pour over the melted butter and some sea salt, then toss with your hands. Scatter over the top of the cheesy leeks and top with a bit more salt. Roast in the oven for 50 minutes. If the rösti browns unevenly, melt a bit more butter and brush it over.
6. When golden and bubbling, remove the dish from the oven, leave for 5 minutes, then serve with leaves.