Preheat the oven to 180°C/350°F. Heat the olive oil over a medium heat and cook the leeks until softened. Remove from the heat and set aside.
Heat the milk in a small saucepan. In another saucepan melt the butter before adding the nutmeg and flour, stirring together to make a roux. Add a little salt before slowly beginning to pour in the warm milk, stirring constantly. Once the sauce is smooth and thick, bring to the boil briefly before removing from the heat.
Cook the pasta for about half the time it instructs on the packet. Place the drained, cooked pasta, leeks, sauce and half the broccoli and asparagus into a large bowl. Mix everything together before tipping into a large, greased baking dish. Scatter the rest of the broccoli and asparagus over the top of the pasta followed by the pancetta and the cheese.
Cook for 20 minutes in the preheated oven. Remove, sprinkle over the breadcrumbs and return to the oven for another 5 minutes until browned. Serve.