Bake four jacket potatoes in the oven for 40 mins before cooking
the leek dish. Split oven and serve the leeks on top.
Heat oven to 200C/fan180C/gas 6. Cook the leeks in a pan of boiling salted water for 4-5 mins or until just tender. Drain and cool under a cold tap to stop them from cooking any further, then drain again well and pat dry on kitchen paper.
Wrap each leek in a slice of ham, then arrange, side-by-side, in a large baking dish. Mix the cheddar in a bowl with the Dijon mustard and crème fraîche, until well combined. Season to taste. Spread over the leeks, then bake for 15-20 mins until bubbling and golden brown. Serve at once with plenty of crusty bread to mop up the juices.