Place the halved leek into boiling salted water and cook until tender. Remove with a slotted spoon and drain well. Place on a baking sheet.
Place the double cream into a pan and simmer until it has reduced by half. Add half of the parmesan and season with black pepper.
Place the torn ham over the top of the cooked leek and then pour over the creamy parmesan sauce. Scatter over the breadcrumbs and the rest of the parmesan and place under the grill until golden-brown and bubbling.
Place the grilled leek on a serving plate and serve immediately.