Gratin van Prei en Ham (Leek and Ham Gratin)

• 50 g Unsalted butter
• 700 g Leek
• 1 tsp Fine sea salt
• ½ tsp Black pepper
• 200 g Cured ham, cooked
• 35 g Plain flour
• 500 ml Whole milk
• 2 tsp Dijon mustard
• ½ tsp Ground nutmeg
• 150 g Gruyère cheese

1. Heat the oven to 200°C (390°F). Butter a baking dish with a little of the unsalted butter.
2. Trim the leeks, slice them into 1 cm rounds, then wash well and drain. Melt 20 g of the butter in a large frying pan over medium heat, add the leeks with the fine sea salt and black pepper, and cook for 10 to 12 minutes until soft and reduced but not browned.
3. Arrange half the softened leeks in the baking dish, then layer over the cured ham. Spoon over the remaining leeks and level the top.
4. In a saucepan over medium heat, melt the remaining butter, then whisk in the plain flour and cook for 1 minute. Gradually whisk in the whole milk until smooth, then simmer gently for 3 to 5 minutes, whisking, until thick enough to coat the back of a spoon.
5. Take the pan off the heat and whisk in the Dijon mustard, ground nutmeg, and about two-thirds of the Gruyère cheese until melted. Taste and adjust with a pinch more fine sea salt and black pepper if needed.
6. Pour the cheese sauce over the leek and ham layers, then sprinkle over the remaining Gruyère cheese. Bake for 20 to 25 minutes until bubbling at the edges and golden on top.
7. Rest for 5 to 10 minutes before serving so the sauce settles and slices neatly. Serve hot.

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