Leek and Ham Gratin

Trim leeks to roughly 18cm lengths, halve lengthways, and rinse thoroughly under cold water, fanning the layers to remove any grit. Grate the Gruyère and set aside. Preheat the oven to 200°C fan (220°C conventional).

Bring a large pot of well-salted water to a rolling boil. Add the leeks and blanch for 6 minutes until just tender but still holding their shape.

Transfer leeks immediately to a bowl of iced water for 2 minutes to stop cooking, then drain on a clean kitchen towel and pat completely dry — excess moisture will thin the béchamel.

Melt 15g of the butter in a wide sauté pan over medium-low heat. Lay the blanched leeks cut-side down in a single layer, season lightly, and cook for 8 minutes until the cut surfaces are golden and the leeks are completely soft and sweet.

Add the white wine to the pan and let it sizzle for 1 minute until evaporated, then remove from heat — the leeks can rest and cool for 5 minutes before rolling.

Lay each ham slice flat, place one leek half at the edge, and roll the ham tightly around it. Arrange the rolls seam-side down in a single layer in a buttered 30 × 20cm gratin dish.

Melt the remaining 40g butter in a medium saucepan over medium heat. Add the flour and whisk constantly for 2 minutes until the roux is pale golden and smells faintly biscuity.

Pour the warm milk into the roux in a slow, steady stream, whisking continuously. Cook for 5 minutes, whisking constantly, until the sauce is thick enough to coat the back of a spoon.

Remove the béchamel from heat and stir in the Dijon mustard, nutmeg, white pepper, and 80g of the Gruyère until fully melted and smooth. Taste and adjust salt.

Pour the béchamel evenly over the ham-wrapped leeks, ensuring every roll is coated. Scatter the remaining 40g Gruyère over the top.

Bake on the upper-middle rack for 25 minutes until the surface is deeply golden and bubbling at the edges. Use a meat thermometer to confirm the ham has reached an internal temperature of at least 63°C before serving.

Rest for 5 minutes before serving, then scatter with chopped parsley.