Macaroni and cheese with sausages

Preheat the oven to 180 ºC (250 ºF). Grease a 31 x 20 cm ovenproof dish with margarine. Boil the macaroni in salted water until soft. Drain and spoon into the prepared dish. Brown the sausages in a little oil and arrange on top of the macaroni. Top with the tomato slices and season lightly with salt and pepper. Make a white sauce: Melt the butter and add the cake flour. Stir to form a smooth paste and heat for about 1 minute while stirring continuously. Remove from the heat and add the milk, a little at a time, stirring continuously. Return to the heat and heat until the white sauce comes to the boil and thickens. Season with mustard powder and salt and pepper to taste. Spoon the sauce over the sausages and tomato slices, spreading it evenly. Combine the Cheddar cheese and breadcrumbs and sprinkle over the dish. Bake for about 30 minutes or until the cheese has melted and the dish is heated through.
Serves 4-6.