Preheat oven to 190°c (375°f), gas 5

Cook the parsnips and leeks in boiling slightly salted water for 10 minutes until just tender. Drain well.

Cook the pasta according to the instructions on the packet and mix with the cooked vegetables.

Place the milk, butter and flour in a saucepan and heat, whisking continually until the sauce thickens and boils.

Season lightly, add the cayenne pepper and mustard and cook for one minute. Remove from the heat and stir in 75g of cheese.

Place half the vegetable mixture in the base of as buttered ovenproof dish, cover with a layer of tomatoes then half the sauce. Repeat the layers, finishing with the sauce.

Mix the remaining cheese with the breadcrumbs and sprinkle over the top.